Systems and methods for dimming control using TRIAC dimmers

ABSTRACT

System and method for dimming control of one or more light emitting diodes. An example system includes one or more signal processing components configured to receive a first signal associated with a TRIAC dimmer, process information associated with the first signal, determine whether the TRIAC dimmer is in a first condition or a second condition, generate a second signal based on at least information associated with the first signal, and send the second signal to a switch. The one or more signal processing components are further configured to, if the TRIAC dimmer is determined to be in the first condition, generate the second signal to cause the switch to be opened and closed corresponding to a modulation frequency.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/710,277, filed Dec. 10, 2012, which claims priority to Chinese PatentApplication No. 201210468505.1, filed Nov. 12, 2012, both applicationsbeing commonly assigned and incorporated by reference herein for allpurposes.

Additionally, this application is related to U.S. patent applicationSer. Nos. 13/105,780 and 13/527,475, both of which are incorporated byreference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for dimmingcontrol using TRIAC dimmers. Merely by way of example, the invention hasbeen applied to systems for driving light emitting diodes (LEDs). But itwould be recognized that the invention has a much broader range ofapplicability.

Lighting systems including light emitting diodes (LEDs) often use aconventional light dimmer (e.g., wall mounted) that includes a Triodefor Alternating Current (TRIAC) to adjust the brightness of LEDs. ATRIAC is bidirectional and currents can flow through a TRIAC in eitherdirection (e.g., into the TRIAC or out of the TRIAC). A TRIAC can betriggered by a gate current (e.g., flowing in either direction) which isoften generated by applying a voltage (e.g., a positive voltage or anegative voltage) to a gate electrode of a TRIAC. Once triggered, theTRIAC continues to conduct a current until the current drops below acertain threshold (e.g., a holding current).

FIG. 1 is a simplified diagram showing a conventional LED lightingsystem using a TRIAC dimmer. For example, the lighting system 100implements a primary side regulation scheme and a flyback structure withsingle-stage power-factor-correction (PFC) for driving one or more LEDs172. The system 100 includes a controller 102, an AC supply component122, a TRIAC dimmer 118, a full wave rectifying bridge 124, capacitors126, 136, 140, 150 and 170, resistors 128, 130, 134, 138, 146, 148, 154and 156, power switches 132 and 152, diodes 142, 144 and 168, and atransformer including a primary winding 162, a secondary winding 164,and an auxiliary winding 166. The controller 102 includes terminals 104,106, 108, 110, 112, 114, 116 and 120. For example, the power switch 132and the power switch 152 are transistors. In another example, a TRIACdimmer 118 is a dimmer that includes a Triode for Alternating Current(TRIAC).

As shown in FIG. 1, the TRIAC dimmer 118 processes an AC input signal121 from the AC supply component 122, and generates a voltage signal 123which is processed by the full wave rectifying bridge 124 in order togenerate a voltage signal 174 (e.g., V_(bulk)). The TRIAC dimmer 118 isassociated with a dimming period including an on period and an offperiod. During an on period of the TRIAC dimmer 118, the voltage signal174 is approximately equal to the AC input signal 121 in magnitude.During an off period of the TRIAC dimmer 118, the voltage signal 174 hasa low magnitude (e.g., approximately zero). The capacitor 150 (e.g., C₁)is charged in response to the voltage signal 174 (e.g., V_(bulk))through the resistor 138 (e.g., R₃), and a voltage signal 176 isgenerated at the terminal 112 (e.g., terminal VCC). If the voltagesignal 176 exceeds an under-voltage-lock-out (UVLO) threshold voltage,the controller 102 is activated, and outputs a modulation signal 178(e.g., a pulse-width-modulation (PWM) signal) through the terminal 116(e.g., terminal GATE) in order to close (e.g., to turn on) or open(e.g., to turn off) the switch 152 (e.g., M2) for normal operation ofthe system 100. A voltage divider circuit including the resistor 130(e.g., R₂) and the resistor 134 (e.g., R₄) generates a voltage signal179 based on at least information associated with the voltage signal 174(e.g., V_(bulk)). The controller 102 detects the signal 179 at theterminal 106 (e.g., terminal V_(S)) in order to affect the power factorand determine the status of the TRIAC dimmer.

When the controller 102 changes the modulation signal 178 to close(e.g., to turn on) the switch 152 (e.g., M2), a primary current 180flows through the primary winding 162, and a current-sensing signal 188is generated through the resistor 154 (e.g., R_(S)). The controller 102detects the current-sensing signal 188 at the terminal 120 (e.g.,terminal CS). For example, the peak values of the current-sensing signal188 affect the signal 178 to open (e.g., to turn off) the switch 152 ineach cycle. An auxiliary current 182 flows through the auxiliary winding166 to charge the capacitor 150 (e.g., C₁), and a voltage signal 184 isgenerated at the auxiliary winding 166. A voltage divider circuitincluding the resistor 146 (e.g., R₅) and the resistor 148 (e.g., R₆)generates a voltage signal 186 based on at least information associatedwith the voltage signal 184. The controller 102 receives the signal 186at the terminal 114 (e.g., terminal ZCD) in order to detect the end of ademagnetization process associated with the transformer including thesecondary winding 164. In addition, the capacitor 170 is used tomaintain output voltage for stable current output to the LEDs 172.During the on period of the TRIAC dimmer 118, the power switch 132(e.g., M1) is open (e.g., off). During the off period of the TRIACdimmer 118, the power switch 132 is closed (e.g., on) to provide ableeding current in order for the TRIAC dimmer 118 to operate normally.

FIG. 2 is a simplified conventional diagram of the controller 102 asshown in FIG. 1. The controller 102 includes a comparator 202, an erroramplifier including a comparator 204 and a switch 205, a logic controlcomponent 206, a gate drive component 208, a signal generator 210 (e.g.,a PWM signal generator), a multiplier 212, and a current regulationcomponent 214. For example, the PWM signal generator is configured togenerate one or more pulse-width-modulation signals. In another example,the PWM signal generator includes a comparator.

As shown in FIG. 1 and FIG. 2, the comparator 204 receives the signal179 and a threshold signal 226 in order to detect the status of theTRIAC dimmer 118, and outputs a dimming signal 228. The switch 205 isclosed or open in response to the dimming signal 228 to affect theoutput current in order to adjust the brightness of the LEDs 172 (e.g.,to adjust the brightness of the LEDs 172 linearly as a function of theoutput current). The current regulation component 214 receives thecurrent sensing signal 188 at the terminal 120 (e.g., terminal CS) todetect the peak values of the primary current 180, and integrates thepeak values of the primary current 180 over a demagnetization periodassociated with the transformer including the primary winding 162 andthe secondary winding 164. The multiplier 212 receives a processedsignal 216 from the current regulation component 214 and the voltagesignal 179 from the terminal 106 (e.g., terminal VS) and generates anoutput signal 218.

The signal generator 210 receives the current sensing signal 188 and theoutput signal 218 and generates a signal 220. During an operating cycle,if the modulation signal 178 is at a logic high level and the switch 152is closed (e.g., turned on), the primary current 180 flowing through theswitch 152 increases in magnitude. In response the current sensingsignal 188 increases in magnitude. If the signal 188 becomes larger thanthe output signal 218 in magnitude, the signal generator 210 changes thesignal 220 and the controller 102 changes the signal 178 from the logichigh level to a logic low level to open (e.g., to turn off) the switch152. When the switch 152 is opened (e.g., turned off), the transformerincluding the primary winding 162 and the secondary winding 164 beginsthe demagnetization process.

The comparator 202 receives the signal 186 and a threshold signal 222 todetect whether the demagnetization process has completed. If thedemagnetization process is determined to be completed, the comparator202 outputs a signal 224 in order to change the signal 178 to the logichigh level. During the off period of the TRIAC dimmer 118, the logiccontrol component 206 outputs a signal 230 to close (e.g., to turn on)the switch 132 (e.g., M1) in order to provide a bleeding current for thenormal operation of the TRIAC dimmer 118.

The system 100 has some disadvantages. For example, users can perceivethe flickering of the LEDs 172 when the conduction angle of the TRIACdimmer 118 is low (e.g., the portion of the conduction time smaller than20% of an operating period of the TRIAC dimmer 118) or when the AC inputvoltage is high.

Hence it is highly desirable to improve the techniques of dimmingcontrol.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for dimmingcontrol using TRIAC dimmers. Merely by way of example, the invention hasbeen applied to systems for driving light emitting diodes (LEDs). But itwould be recognized that the invention has a much broader range ofapplicability.

According to one embodiment, a system for dimming control of one or morelight emitting diodes includes one or more signal processing componentsconfigured to receive a first signal associated with a TRIAC dimmer,process information associated with the first signal, determine whetherthe TRIAC dimmer is in a first condition or a second condition, generatea second signal based on at least information associated with the firstsignal, and send the second signal to a switch. The one or more signalprocessing components are further configured to, if the TRIAC dimmer isdetermined to be in the first condition, generate the second signal tocause the switch to be opened and closed corresponding to a modulationfrequency, and if the TRIAC dimmer is determined to be in the secondcondition, generate the second signal to cause the switch to remainclosed for a first period of time until at least the TRIAC dimmerchanges from the second condition to the first condition.

According to another embodiment, a system for dimming control of one ormore light emitting diodes includes a first comparator and a drivingcomponent. The first comparator is configured to receive a firstthreshold signal and an input signal associated with a TRIAC dimmer andgenerate a comparison signal based on at least information associatedwith the first threshold signal and the input signal. The drivingcomponent is configured to receive the comparison signal, generate anoutput signal based on at least information associated with thecomparison signal, and send the output signal to a switch. The firstcomparator is further configured to generate the comparison signal at afirst logic level if the input signal is larger than the first thresholdsignal in magnitude and generate the comparison signal at a second logiclevel if the input signal is smaller than the first threshold signal inmagnitude. The driving component is further configured to generate theoutput signal and cause the switch to remain closed for a period of timeuntil at least the comparison signal changes from the second logic levelto the first logic level.

According to yet another embodiment, a system for dimming control of oneor more light emitting diodes includes a first comparator, a detectioncomponent, and a driving component. The first comparator is configuredto receive a first threshold signal and a first signal associated with aTRIAC dimmer and generate a first comparison signal based on at leastinformation associated with the first threshold signal and the firstsignal. The detection component is configured to receive the firstcomparison signal, determine a duty cycle of the first comparisonsignal, process information associated with the duty cycle and athreshold value, and generate a detection signal based on at leastinformation associated with the first comparison signal. The drivingcomponent is configured to receive the detection signal, generate asecond signal based on at least information associated with thedetection signal, and output the second signal to a switch. The firstcomparator is further configured to generate the first comparison signalat a first logic level if the first signal is larger than the thresholdsignal in magnitude and generate the first comparison signal at a secondlogic level if the first signal is smaller than the threshold signal inmagnitude. The detection component is further configured to generate thedetection signal at a third logic level if the duty cycle of the firstcomparison signal is larger than the threshold value in magnitude andgenerate the detection signal at a fourth logic level if the duty cycleof the first comparison signal is smaller than the threshold value inmagnitude. The driving component is further configured to, if thedetection signal is at the fourth logic level, generate the secondsignal to cause the switch to remain open for a first period of time.

According to yet another embodiment, a system for detecting a duty cycleof a signal includes a voltage generator, a comparator, and a signalgenerator. The voltage generator is configured to receive an inputsignal and generate a first voltage signal based on at least informationassociated with the input signal. The comparator is configured toreceive the first voltage signal and a threshold signal and generate acomparison signal based on at least information associated with thefirst voltage signal and the threshold signal. The signal processor isconfigured to receive the comparison signal and the input signal andgenerate an output signal based on at least information associated withthe comparison signal and the input signal. The comparator is furtherconfigured to, if the first voltage signal is larger than the thresholdsignal in magnitude, generate the comparison signal at a first logiclevel, and if the first voltage signal is smaller than the thresholdsignal in magnitude, generate the comparison signal at a second logiclevel. The signal processor is further configured to, if a duty cycle ofthe input signal is larger than a threshold value, generate the outputsignal at a third logic level, and if the duty cycle of the input signalis smaller than the threshold value, generate the output signal at afourth logic level. The signal processor is further configured to, ifthe input signal changes from a fifth logic level to a sixth logic leveland if the comparison signal is at the first logic level, change theoutput signal from the third logic level to the fourth logic level.

In one embodiment, a method for dimming control of one or more lightemitting diodes includes, receiving a first signal associated with aTRIAC dimmer, processing information associated with the first signal,and determining whether the TRIAC dimmer is in a first condition or asecond condition based on at least information associated with the firstsignal. The method further includes generating a second signal based onat least information associated with the first signal, and outputtingthe second signal to a switch. The process for generating a secondsignal based on at least information associated with the first signalincludes, if the TRIAC dimmer is determined to be in the firstcondition, generating the second signal to cause the switch to be openedand closed corresponding to a modulation frequency, and if the TRIACdimmer is determined to be in the second condition, generating thesecond signal to cause the switch to remain closed for a first period oftime until at least the TRIAC dimmer changes from the second conditionto the first condition.

In another embodiment, a method for dimming control of one or more lightemitting diodes includes, receiving a threshold signal and an inputsignal associated with a TRIAC dimmer, generating a comparison signalbased on at least information associated with the first threshold signaland the input signal, and receiving the comparison signal. The methodfurther includes generating an output signal based on at leastinformation associated with the comparison signal and sending the outputsignal to a switch. The process for generating a comparison signal basedon at least information associated with the first threshold signal andthe input signal includes, if the input signal is larger than the firstthreshold signal in magnitude, generating the comparison signal at afirst logic level, and if the input signal is smaller than the firstthreshold signal in magnitude, generating the comparison signal at asecond logic level. The process for sending the output signal to aswitch includes sending the output signal to cause the switch to remainclosed for a period of time until at least the comparison signal changesfrom the second logic level to the first logic level.

In yet another embodiment, a method for dimming control of one or morelight emitting diodes includes receiving a threshold signal and an inputsignal associated with a TRIAC dimmer, generating a comparison signalbased on at least information associated with the threshold signal andthe input signal, and receiving the comparison signal. The methodfurther includes determining a duty cycle of the comparison signal,processing information associated with the duty cycle and a thresholdvalue, and generating a detection signal based on at least informationassociated with the comparison signal. In addition, the method includesreceiving the detection signal, generating an output signal based on atleast information associated with the detection signal, and sending theoutput signal to a switch. The process for generating a comparisonsignal based on at least information associated with the thresholdsignal and the input signal includes, if the input signal is larger thanthe threshold signal in magnitude, generating the comparison signal at afirst logic level, and if the input signal is smaller than the thresholdsignal in magnitude, generating the comparison signal at a second logiclevel. The process for generating a detection signal based on at leastinformation associated with the comparison signal includes, if the dutycycle of the comparison signal is larger than the threshold value inmagnitude, generating the detection signal at a third logic level, andif the duty cycle of the comparison signal is smaller than the thresholdvalue in magnitude, generating the detection signal at a fourth logiclevel. The process for generating an output signal based on at leastinformation associated with the detection signal includes if thedetection signal is at the fourth logic level, generating the outputsignal to cause the switch to remain open for a first period of time.

In yet another embodiment, a method for detecting a duty cycle of asignal includes receiving an input signal, generating a first voltagesignal based on at least information associated with the input signal,and receiving the first voltage signal and a threshold signal. Themethod further includes generating a comparison signal based on at leastinformation associated with the first voltage signal and the thresholdsignal, receiving the comparison signal and the input signal, andgenerating an output signal based on at least information associatedwith the comparison signal and the input signal. The process forgenerating a comparison signal based on at least information associatedwith the first voltage signal and the threshold signal includes, if thefirst voltage signal is larger than the threshold signal in magnitude,generating the comparison signal at a first logic level, and if thefirst voltage signal is smaller than the threshold signal in magnitude,generating the comparison signal at a second logic level. The processfor generating an output signal based on at least information associatedwith the comparison signal and the input signal includes, if a dutycycle of the input signal is larger than a threshold value, generatingthe output signal at a third logic level, if the duty cycle of the inputsignal is smaller than the threshold value, generating the output signalat a fourth logic level, and if the input signal changes from a fifthlogic level to a sixth logic level and if the comparison signal is atthe first logic level, changing the output signal from the third logiclevel to the fourth logic level.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a conventional LED lightingsystem using a TRIAC dimmer.

FIG. 2 is a simplified conventional diagram of the controller as shownin FIG. 1.

FIG. 3 is a simplified diagram showing a lighting system according to anembodiment of the present invention.

FIG. 4 is a simplified diagram of the system controller as part of thesystem as shown in FIG. 3 according to an embodiment of the presentinvention.

FIG. 5 shows simplified timing diagrams for the system as shown in FIG.3 according to an embodiment of the present invention.

FIG. 6 is a simplified diagram showing the system controller as part ofthe system as shown in FIG. 3 according to another embodiment of thepresent invention.

FIG. 7 is a simplified diagram showing the system controller as part ofthe system as shown in FIG. 3 according to yet another embodiment of thepresent invention.

FIG. 8 shows simplified timing diagrams analyzing disadvantages of theconventional LED lighting system as shown in FIG. 1.

FIG. 9(a) is a simplified diagram showing the system controller as partof the system as shown in FIG. 3 according to another embodiment of thepresent invention.

FIG. 9(b) is a simplified diagram showing the system controller as partof the system as shown in FIG. 3 according to yet another embodiment ofthe present invention.

FIG. 9(c) is a simplified diagram showing the system controller as partof the system as shown in FIG. 3 according to yet another embodiment ofthe present invention.

FIG. 10 is a simplified diagram showing certain components of the systemcontroller as part of the system as shown in FIG. 9(a), FIG. 9(b),and/or FIG. 9(c) according to some embodiments of the present invention.

FIG. 11 is a simplified diagram showing certain components of thedetection component as part of the system controller as shown in FIG. 10according to an embodiment of the present invention.

FIG. 12(a) shows simplified timing diagrams for the detection componentas part of the system controller for the system as shown in FIG. 10 ifthe dimming signal has a large duty cycle.

FIG. 12(b) shows simplified timing diagrams for the detection componentas part of the system controller for the system as shown in FIG. 10 ifthe dimming signal has a small duty cycle according to some embodimentsof the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for dimmingcontrol using TRIAC dimmers. Merely by way of example, the invention hasbeen applied to systems for driving light emitting diodes (LEDs). But itwould be recognized that the invention has a much broader range ofapplicability.

An important parameter of a TRIAC dimmer is a holding current whichindicates a minimum current for normal operation of the TRIAC dimmer. Ifa TRIAC dimmer is used for driving resistive loads (e.g., incandescentlamps), the holding current requirement can be easily satisfied. But ifa TRIAC dimmer is used for driving capacitive loads (e.g., LEDs),additional circuits or components may be needed for satisfying theholding current requirement. For example, as shown in FIG. 1, the switch132 (e.g., M1) is used for providing a holding current during the offperiod of the TRIAC dimmer. But the system 100 implements an additionalpower switch (e.g., M1) and an extra pin (e.g., terminal TRIAC) on thecontroller 102 which increases the control complexity and system cost.

FIG. 3 is a simplified diagram showing a lighting system according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. The system 300 includes a system controller 302, an ACsupply component 322, a TRIAC dimmer 318, a full wave rectifying bridge324, capacitors 326, 336, 340, 350 and 370, resistors 330, 334, 338,346, 348, 354 and 356, a power switch 352, diodes 342, 344 and 368, anda transformer including a primary winding 362, a secondary winding 364,and an auxiliary winding 366. The system controller 302 includesterminals 306, 308, 310, 312, 314, 316 and 320. For example, the powerswitch 352 is a transistor.

As shown in FIG. 3, a voltage signal 374 (e.g., V_(bulk)) is generatedwhen an AC input signal 321 from the AC supply component 322 isprocessed by the TRIAC dimmer 318 and the rectifying bridge 324according to certain embodiments. For example, the TRIAC dimmer 318 isassociated with a dimming period including an on period and an offperiod. In another example, during an on period of the TRIAC dimmer 318,the voltage signal 374 is approximately equal to the AC input signal 321in magnitude. In yet another example, during an off period of the TRIACdimmer 318, the voltage signal 374 has a low magnitude (e.g.,approximately zero). In yet another example, the capacitor 350 (e.g.,C₁) is charged in response to the voltage signal 374 (e.g., V_(bulk))through the resistor 338 (e.g., R₃), and a voltage signal 376 isgenerated at the terminal 312 (e.g., terminal VCC). In yet anotherexample, the TRIAC dimmer 318 is under an on condition during the onperiod, and under an off condition during the off period.

According to certain embodiments, if the voltage signal 376 exceeds anunder-voltage-lock-out (UVLO) threshold voltage, the system controller302 is activated, and outputs a control signal 378 through the terminal316 in order to close (e.g., to turn on) or open (e.g., to turn off) theswitch 352 (e.g., M2). For example, the control signal 378 is apulse-width-modulation (PWM) signal to close (e.g., to turn on) or open(e.g., to turn off) the switch 352 for normal operation of the system300.

In one embodiment, the switch 352 is a field effect transistor, whichcan be closed (e.g., turned on) or opened (e.g., turned off) by thecontrol signal 378. For example, the control signal 378 is a voltagesignal. In another example, if the control signal 378 is at the logichigh level, the field effect transistor is closed (e.g., turned on). Inyet another example, if the control signal 378 is at the logic lowlevel, the field effect transistor is opened (e.g., turned off).

In another embodiment, the switch 352 is a bipolar junction transistor,which can be closed (e.g., turned on) or opened (e.g., turned off) bythe control signal 378. For example, the control signal 378 is a currentsignal. In another example, if the control signal 378 is at a highcurrent level, the bipolar transistor is closed (e.g., turned on). Inyet another example, if the control signal 378 is at a low currentlevel, the field effect transistor is opened (e.g., turned off).

For example, a voltage divider circuit including the resistor 330 (e.g.,R₂) and the resistor 334 (e.g., R₄) generates a voltage signal 379 basedon at least information associated with the voltage signal 374 (e.g.,V_(bulk)). In another example, the system controller 302 detects thesignal 379 at the terminal 306 (e.g., terminal V_(S)) in order to affectthe power factor and determine the status of the TRIAC dimmer.

According to another embodiment, when the system controller 302 changesthe signal 378 to close (e.g., to turn on) the switch 352 (e.g., M2), aprimary current 380 flows through the primary winding 362, and acurrent-sensing signal 388 is generated through the resistor 354 (e.g.,R_(S)). For example, the system controller 302 detects thecurrent-sensing signal 388 at the terminal 320 (e.g., terminal CS). Inanother example, the peak values of the current-sensing signal 388affect the signal 378 to open (e.g., to turn off) the switch 352 in eachcycle. In yet another example, an auxiliary current 382 flows throughthe auxiliary winding 366 to charge the capacitor 350, and a voltagesignal 384 is generated at the auxiliary winding 366. In yet anotherexample, a voltage divider circuit including the resistor 346 and theresistor 348 generates a voltage signal 386 based on at leastinformation associated with the voltage signal 384. In yet anotherexample, the system controller 302 receives the signal 386 at theterminal 314 (e.g., terminal ZCD) in order to detect the end of ademagnetization process associated with the transformer including thesecondary winding 364. In yet another example, during the off period ofthe TRIAC dimmer 318, the system controller 302 outputs the signal 378to close (e.g., to turn on) the power switch 352 (e.g., M2) to provide acurrent flow path in order for the TRIAC dimmer 318 to operate normally.In yet another example, the capacitor 370 is used to maintain outputvoltage for stable current output to the LEDs 372.

FIG. 4 is a simplified diagram of the system controller 302 as part ofthe system 300 according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The system controller 302includes a comparator 402, an error amplifier including a comparator 404and a switch 405, a logic control component 406, a gate drive component408, a signal generator 410 (e.g., a PWM signal generator), a multiplier412, and a current regulation component 414.

As shown in FIG. 3 and FIG. 4, the comparator 404 receives the signal379 and a threshold signal 426 in order to detect the status of theTRIAC dimmer 318, and outputs a dimming signal 428 in some embodiments.For example, if the dimming signal 428 is at the logic high level, theswitch 405 is closed or open to affect the output current in order toadjust the brightness of the LEDs 372 (e.g., linearly). In anotherexample, the current regulation component 414 receives the currentsensing signal 388 at the terminal 320 (e.g., terminal CS) to detect thepeak values of the primary current 380, and integrates the peak valuesof the primary current 380 over a demagnetization period associated withthe transformer that includes the primary winding 362 and the secondarywinding 364. In yet another example, the multiplier 412 receives aprocessed signal 416 from the current regulation component 414 and thevoltage signal 379 from the terminal 306 (e.g., terminal VS) andgenerates an output signal 418.

According to one embodiment, the signal generator 410 receives thecurrent sensing signal 388 and the output signal 418 and generates asignal 420. For example, during an operating cycle, if the switch 352 isclosed (e.g., turned on) in response to the signal 378, the primarycurrent 380 flowing through the switch 352 increases in magnitude, andin response the current sensing signal 388 also increases in magnitude.In yet another example, if the signal 388 becomes larger than the outputsignal 418 in magnitude, the signal generator 410 changes the signal 420and the system controller 302 changes the signal 378 in order to open(e.g., to turn off) the switch 352.

According to another embodiment, the comparator 402 receives the signal386 and a threshold signal 422 to detect whether the demagnetizationprocess has completed. For example, if the demagnetization process isdetermined to be completed, the comparator 402 outputs a signal 424 tochange the signal 378 in order to close (e.g., turn on) the switch 352.In another example, the logic control component 406 receives the signal424, the dimming signal 428 and the signal 420 and outputs a signal 430to the gate drive component 408.

In one embodiment, if the dimming signal 428 is at the logic high level(e.g., during the on period of the TRIAC dimmer 318), in response to thesignals 420 and 424, the logic control component 406 changes the signal430 between the logic high level and the logic low level to affect thesignal 378 in order to close (e.g., to turn on) or open (e.g., to turnoff) the switch 352 corresponding to a modulation frequency. Forexample, the modulation frequency is equal to 1 divided by acorresponding modulation period.

In another embodiment, if the dimming signal 428 is at the logic lowlevel (e.g., during the off period of the TRIAC dimmer 318), the logiccontrol component 406 keeps the signal 430 at the logic high level toaffect the signal 378 in order to keep the switch 352 closed (e.g., on)for a first period of time. For example, the first period of time isequal to or larger than the modulation period. In another example, thefirst period of time is larger than the modulation period. In yetanother example, the first period of time is equal to, in duration, theoff period of the TRIAC dimmer 318.

FIG. 5 shows simplified timing diagrams for the system 300 according toan embodiment of the present invention. These diagrams are merelyexamples, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The waveform 502 represents the voltage signal 374 asa function of time, the waveform 504 represents the signal 379 as afunction of time, the waveform 506 represents the dimming signal 428 asa function of time, and the waveform 508 represents the signal 378 as afunction of time. Two time periods are shown in FIG. 5, an on timeperiod T_(on1) and an off time period T_(off1). The time period T_(on1)starts at t₀ and ends at t₁, and the time period T_(off1) starts at t₁and ends at t₂. For example, t₀≤t₁≤t₂.

According to one embodiment, at the beginning of the on time period ofthe TRIAC dimmer 318 (e.g., at t₀), the voltage signal 374 (e.g.,V_(bulk)) changes from a low magnitude 509 (e.g., approximately zero) toa large magnitude 511 and the signal 378 changes from a low magnitude514 to a large magnitude 516. For example, the signal 379 (e.g., themagnitude 516) is higher than the threshold signal 426 in magnitude, andin response the comparator 404 changes the dimming signal 428 from alogic low level to a logic high level. In another example, during the ontime period, the voltage signal 374 (e.g., V_(bulk)) and the signal 379decreases in magnitude over time. In yet another example, if the signal379 becomes lower than the threshold signal 426 in magnitude, thecomparator 404 changes the dimming signal 428 from the logic high levelto the logic low level (e.g., at t₁). In yet another example, the systemcontroller 302 outputs the signal 378 which changes between the logiclow level and the logic high level during the on time period. In yetanother example, the signal 378 keeps at the logic high level during theoff time period.

When the AC input signal 321 has a low magnitude, the TRIAC dimmer 318does not suffer much current leakage in certain embodiments. Forexample, during the off period of the TRIAC dimmer 318, the capacitor350 accumulates a small amount of charges and the voltage signal 374(e.g., V_(bulk)) has a low magnitude. In another example, a few pulsesin the signal 378 from the terminal 316 can reduce the voltage signal374 to a low magnitude (e.g., approximately zero), and in response thesignal 379 has a low magnitude (e.g., approximately zero). In yetanother example, the system controller 302 receives the signal 379 atthe terminal 306 to detect the status of the TRIAC dimmer 318 in orderfor the error amplifier including the comparator 204 to operatenormally. In yet another example, during the off period of the TRIACdimmer 318, the current sensing signal 388 has low peak values (e.g.,approximately zero) and in response the signal generator 410 changes thesignal 420 in order to keep the signal 378 at the logic high level.

FIG. 6 is a simplified diagram showing the system controller 302 as partof the system 300 according to another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The systemcontroller 302 includes a comparator 602, an error amplifier including acomparator 604 and a switch 605, a logic control component 606, a gatedrive component 608, a signal generator 610 (e.g., a PWM signalgenerator), a multiplier 612, a current regulation component 614, and anoffset component 615.

As shown in FIG. 3 and FIG. 6, the comparator 604 receives the signal379 and a threshold signal 626 in order to detect the status of theTRIAC dimmer 318, and outputs a dimming signal 628 in some embodiments.For example, the switch 605 is closed or open in response to the dimmingsignal 628 to affect the output current in order to adjust thebrightness of the LEDs 372 (e.g., linearly). In another example, thecurrent regulation component 614 receives the current sensing signal 388at the terminal 320 (e.g., terminal CS) to detect the peak values of theprimary current 380, and integrates the peak values of the primarycurrent 380 over a demagnetization period associated with thetransformer including the primary winding 362 and the secondary winding364. In yet another example, the multiplier 612 receives a processedsignal 616 from the current regulation component 614 and the voltagesignal 379 from the terminal 306 (e.g., terminal VS) and outputs asignal 618 to the offset component 615. In yet another example, thesignal processor 610 receives the current sensing signal 388 and asignal 619 from the offset component 615 and outputs a signal 620.

According to one embodiment, the comparator 602 receives the signal 386and a threshold signal 622 to detect whether the demagnetization processhas completed. For example, if the demagnetization process is determinedto be completed, the comparator 602 outputs a signal 624 to change thesignal 378 in order to close (e.g., to turn on) the switch 352. Inanother example, the logic control component 606 receives the signal624, the dimming signal 628 and the signal 620 and outputs a signal 630to the gate drive component 608.

In one embodiment, if the dimming signal 628 is at the logic high level(e.g., during the on period of the TRIAC dimmer 318), in response to thesignals 620 and 624, the logic control component 606 changes the signal630 between the logic high level and the logic low level to affect thesignal 378 in order to close (e.g., to turn on) or open (e.g., to turnoff) the switch 352 corresponding to a modulation frequency. Forexample, the modulation frequency is equal to 1 divided by acorresponding modulation period.

In another embodiment, if the dimming signal 628 is at the logic lowlevel (e.g., during the off period of the TRIAC dimmer 318), the logiccontrol component 606 keeps the signal 630 at the logic high level toaffect the signal 378 in order to keep the switch 352 closed (e.g., on)for a first period of time. For example, the first period of time isequal to or larger than the modulation period. In another example, thefirst period of time is larger than the modulation period. In yetanother example, the first period of time is equal to, in duration, theoff period of the TRIAC dimmer 318.

In yet another embodiment, when the AC input signal 321 has a largemagnitude, the TRIAC dimmer 318 has a high current leakage and thecapacitor 326 accumulates a large amount of charges during the offperiod of the TRIAC dimmer 318. For example, if pulses in the signal 378cannot pull the signal 374 (e.g., V_(bulk)) down to a low magnitude(e.g., approximately zero), the signal 379 has a magnitude larger thanzero. In another example, the current sensing signal 388 has peak valueslarger than zero during the off period of the TRIAC dimmer 318. In yetanother example, because the offset component 615 adds a predeterminedoffset to the signal 618 to generate the signal 619, the current sensingsignal 388 is kept smaller than the signal 619 in magnitude and inresponse the signal processor 610 outputs the signal 620 to affect thesignal 378 in order to keep the switch 352 closed (e.g., on) during theoff period of the TRIAC dimmer 318. In yet another example, the signal374 (e.g., V_(bulk)) can be pulled down to a low magnitude (e.g.,approximately zero) to keep the signal 378 stable so that the LEDs 372do not flicker during the off period of the TRIAC dimmer 318.

FIG. 7 is a simplified diagram showing the system controller 302 as partof the system 300 according to yet another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The systemcontroller 302 includes comparators 702 and 711, an error amplifierincluding a comparator 704 and a switch 705, a logic control component706, a gate drive component 708, a signal generator 710 (e.g., a PWMsignal generator), a multiplier 712, and a current regulation component714.

As shown in FIG. 3 and FIG. 7, the comparator 704 receives the signal379 and a threshold signal 726 in order to detect the status of theTRIAC dimmer 318, and outputs a dimming signal 728 in some embodiments.For example, the switch 705 is closed or open in response to the dimmingsignal 728 to affect the output current in order to adjust thebrightness of the LEDs 372 (e.g., linearly). In another example, thecurrent regulation component 714 receives the current sensing signal 388at the terminal 320 (e.g., terminal CS) to detect the peak values of theprimary current 380, and integrates the peak values of the primarycurrent 380 over a demagnetization period associated with thetransformer including the primary winding 362 and the secondary winding364. In yet another example, the multiplier 712 receives a processedsignal 716 from the current regulation component 714 and the voltagesignal 379 from the terminal 306 (e.g., terminal VS) and generates anoutput signal 718. In yet another example, the signal generator 710receives the current sensing signal 388 and the output signal 718 andgenerates a signal 720.

According to one embodiment, the comparator 702 receives the signal 386and a threshold signal 722 to detect whether the demagnetization processhas completed. For example, if the demagnetization process is determinedto be completed, the comparator 702 outputs a signal 724 to change thesignal 378 in order to close (e.g., to turn on) the switch 352. Inanother example, the logic control component 706 receives the signal724, the dimming signal 728 and the signal 720 and outputs a signal 730to the gate drive component 708.

In one embodiment, if the dimming signal 728 is at the logic high level(e.g., during the on period of the TRIAC dimmer 318), in response to thesignals 720 and 724, the logic control component 706 changes the signal730 between the logic high level and the logic low level to affect thesignal 378 in order to close (e.g., to turn on) or open (e.g., to turnoff) the switch 352 corresponding to a modulation frequency. Forexample, the modulation frequency is equal to 1 divided by acorresponding modulation period.

In another embodiment, if the dimming signal 728 is at the logic lowlevel (e.g., during the off period of the TRIAC dimmer 318), the logiccontrol component 706 keeps the signal 730 at the logic high level toaffect the signal 378 in order to keep the switch 352 closed (e.g., on)for a first period of time. For example, the first period of time isequal to or larger than the modulation period. In another example, thefirst period of time is larger than the modulation period. In yetanother example, the first period of time is equal to, in duration, theoff period of the TRIAC dimmer 318.

In yet another embodiment, the comparator 711 receives the currentsensing signal 388 at the terminal 320 (e.g., terminal CS) and athreshold signal 731 and outputs a comparison signal 733 to the logiccontrol component 706. For example, if the current sensing signal 388 issmaller than the threshold signal 731 in magnitude, the comparator 711changes the comparison signal 733 in order to change the signal 378 inorder to turn on the switch 352 (e.g., M2). Thus, the voltage signal 374(e.g., V_(bulk)) is pulled down to a low magnitude (e.g., approximatelyzero) to keep the signal 378 stable so that the LEDs 372 do not flickerduring the off period of the TRIAC dimmer 318, even if the AC inputsignal 321 has a large magnitude, in certain embodiments. For example,if the current sensing signal 388 is larger than the threshold signal731 in magnitude, the status of the signal 378 is affected by the signal720 which is generated based on at least information associated with thesignal 718 and the current sensing signal 388.

As discussed above, and further emphasized here, FIG. 4, FIG. 5, FIG. 6and FIG. 7 are merely examples, which should not unduly limit the scopeof the claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, the operationof certain components of the system controller 302 illustrated in FIG. 4also applies to the system controller 302 as shown in FIG. 6 and/or FIG.7. In another example, the system controller 302 as shown in FIG. 6 orthe system controller 302 as shown in FIG. 7 has timing diagrams similarto those as shown in FIG. 5.

FIG. 8 shows simplified timing diagrams analyzing disadvantages of theconventional LED lighting system 100. The waveform 802 represents the ACinput signal 121 as a function of time, the waveform 804 represents avoltage signal 123 as a function of time, the waveform 806 representsthe voltage signal 174 in ideality as a function of time, and thewaveform 808 represents the voltage signal 174 in reality as a functionof time.

Referring back to FIG. 1, the TRIAC dimmer 118, because of its intrinsiccharacteristics, processes positive values and negative values in the ACinput signal 121 differently to generate the voltage signal 123 (e.g.,as shown by the waveform 804). Ideally, the voltage signal 174 (e.g.,V_(bulk)) has a same waveform during each on time period of the TRIACdimmer 118 (e.g., as shown by the waveform 806). But in reality, thewaveform of the voltage signal 174 (e.g., V_(bulk)) during each on timeperiod of the TRIAC dimmer 118 varies over time (e.g., as shown by thewaveform 808). Such variance affects the output current of the system100. If the conduction angle of the TRIAC dimmer 118 is large, the LEDs172 are bright enough so that human observers can hardly perceive anyflickering. But if the conduction angle of the TRIAC dimmer 118 issmall, the LEDs 172 are not very bright. If the current flowing throughthe LEDs 172 varies in different operating periods, human observers canperceive the flickering of the LEDs 172.

FIG. 9(a) is a simplified diagram showing the system controller 302 aspart of the system 300 according to another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The systemcontroller 302 includes a comparator 902, an error amplifier including acomparator 904 and a switch 905, a logic control component 906, a gatedrive component 908, a signal generator 910 (e.g., a PWM signalgenerator), a multiplier 912, a current regulation component 914, and adetection component 911. For example, the comparator 902, the comparator904, the switch 905, the logic control component 906, the gate drivecomponent 908, the signal generator 910, the multiplier 912, and thecurrent regulation component 914 are the same as the comparator 402, thecomparator 404 and the switch 405, the logic control component 406, thegate drive component 408, the signal generator 410, the multiplier 412,and the current regulation component 414.

As shown in FIG. 3 and FIG. 9(a), the comparator 904 receives the signal379 and a threshold signal 926 in order to detect the status of theTRIAC dimmer 318, and outputs a dimming signal 928 (e.g., the signal428) in some embodiments. For example, the switch 905 is closed or openin response to the dimming signal 928 to affect the output current inorder to adjust the brightness of the LEDs 372 (e.g., linearly). Inanother example, the current regulation component 914 receives thecurrent sensing signal 388 at the terminal 320 (e.g., terminal CS) todetect the peak values of the primary current 380, and integrates thepeak values of the primary current 380 over a demagnetization periodassociated with the transformer including the primary winding 362 andthe secondary winding 364. In yet another example, the multiplier 912receives a processed signal 916 (e.g., the signal 416) from the currentregulation component 914 and the voltage signal 379 from the terminal306 (e.g., terminal VS) and outputs a signal 918 (e.g., the signal 418).In yet another example, the signal processor 910 receives the currentsensing signal 388 and the signal 918 and outputs a signal 920 (e.g.,the signal 420).

According to another embodiment, a duty cycle of the dimming signal 928represents the conduction angle of the TRIAC dimmer 318. For example,the detection component 911 receives the dimming signal 928 to determinethe duty cycle of the dimming signal 928 and outputs a signal 933 to thelogic control component 906. In another example, if the duty cycle ofthe dimming signal 928 is determined to be smaller than a threshold, thesystem controller 302 is configured to change the signal 378 to open(e.g., to turn off) the switch 352 in order to turn off the system 300.In yet another example, the comparator 902 receives the signal 386 and athreshold signal 922 to detect whether the demagnetization process hascompleted. In yet another example, if the demagnetization process isdetermined to be completed, the comparator 902 outputs a signal 924(e.g., the signal 424) to the logic control component 906 which alsoreceives the dimming signal 928 and the signal 920 and outputs a signal930 to the gate drive component 908.

FIG. 9(b) is a simplified diagram showing the system controller 302 aspart of the system 300 according to yet another embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thesystem controller 302 includes a comparator 1002, an error amplifierincluding a comparator 1004 and a switch 1005, a logic control component1006, a gate drive component 1008, a signal generator 1010 (e.g., a PWMsignal generator), a multiplier 1012, a current regulation component1014, a detection component 1011 and an offset component 1015. Forexample, the comparator 1002, the comparator 1004, the switch 1005, thelogic control component 1006, the gate drive component 1008, the signalgenerator 1010, the multiplier 1012, the current regulation component1014, and the offset component 1015 are the same as the comparator 602,the comparator 604 and the switch 605, the logic control component 606,the gate drive component 608, the signal generator 610, the multiplier612, the current regulation component 614, and the offset component 615.

As shown in FIG. 3 and FIG. 9(b), the comparator 1004 receives thesignal 379 and a threshold signal 1026 in order to detect the status ofthe TRIAC dimmer 318, and outputs a dimming signal 1028 (e.g., thesignal 628) in some embodiments. For example, the switch 1005 is closedor open in response to the dimming signal 1028 to affect the outputcurrent in order to adjust the brightness of the LEDs 372 (e.g.,linearly). In another example, the current regulation component 1014receives the current sensing signal 388 at the terminal 320 (e.g.,terminal CS) to detect the peak values of the primary current 380, andintegrates the peak values of the primary current 380 over ademagnetization period associated with the transformer including theprimary winding 362 and the secondary winding 364. In yet anotherexample, the multiplier 1012 receives a processed signal 1016 (e.g., thesignal 616) from the current regulation component 1014 and the voltagesignal 379 from the terminal 306 (e.g., terminal VS) and outputs asignal 1018 to the offset component 1015. In yet another example, thesignal processor 910 receives the current sensing signal 388 and asignal 1019 (e.g., the signal 619) from the offset component 1015 andoutputs a signal 1020 (e.g., the signal 920) to the logic controlcomponent 1006.

According to another embodiment, a duty cycle of the dimming signal 1028represents the conduction angle of the TRIAC dimmer 318. For example,the detection component 1011 receives the dimming signal 1028 todetermine the duty cycle of the dimming signal 1028 and outputs a signal1033 to the logic control component 1006. In another example, if theduty cycle of the dimming signal 1028 is determined to be smaller than athreshold, the system controller 302 is configured to change the signal378 to open (e.g., to turn off) the switch 352 in order to turn off thesystem 300. In yet another example, the comparator 1002 receives thesignal 386 and a threshold signal 1022 to detect whether thedemagnetization process has completed. In yet another example, if thedemagnetization process is determined to be completed, the comparator1002 outputs a signal 1024 (e.g., the signal 624) to the logic controlcomponent 1006 which outputs a signal 1030 to the gate drive component1008.

FIG. 9(c) is a simplified diagram showing the system controller 302 aspart of the system 300 according to yet another embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thesystem controller 302 includes a comparator 1102, an error amplifierincluding a comparator 1104 and a switch 1105, a logic control component1106, a gate drive component 1108, a signal generator 1110 (e.g., a PWMsignal generator), a multiplier 1112, a current regulation component1114, a detection component 1111 and a comparator 1115. For example, thecomparator 1102, the comparator 1104, the switch 1105, the logic controlcomponent 1106, the gate drive component 1108, the signal generator1110, the multiplier 1112, the current regulation component 1114, andthe comparator 1115 are the same as the comparator 702, the comparator704, the switch 705, the logic control component 706, the gate drivecomponent 708, the signal generator 710, the multiplier 712, the currentregulation component 714, and the comparator 711.

As shown in FIG. 3 and FIG. 9(c), the comparator 1104 receives thesignal 379 and a threshold signal 1126 in order to detect the status ofthe TRIAC dimmer 318, and outputs a dimming signal 1128 (e.g., thesignal 728) in some embodiments. For example, the switch 1105 is closedor open in response to the dimming signal 1128 to affect the outputcurrent in order to adjust the brightness of the LEDs 372 (e.g.,linearly). In another example, the current regulation component 1114receives the current sensing signal 388 at the terminal 320 (e.g.,terminal CS) to detect the peak values of the primary current 380, andintegrates the peak values of the primary current 380 over ademagnetization period associated with the transformer including theprimary winding 362 and the secondary winding 364. In yet anotherexample, the multiplier 1112 receives a processed signal 1116 (e.g., thesignal 716) from the current regulation component 1114 and the voltagesignal 379 from the terminal 306 (e.g., terminal VS) and outputs asignal 1118 (e.g., the signal 718) to the signal processor 1110. In yetanother example, the signal processor 1110 receives the current sensingsignal 388 and the signal 1118 and outputs a signal 1120 (e.g., thesignal 720) to the logic control component 1106.

According to another embodiment, a duty cycle of the dimming signal 1128represents the conduction angle of the TRIAC dimmer 318. For example,the detection component 1111 receives the dimming signal 1128 todetermine the duty cycle of the dimming signal 1128 and outputs a signal1133 to the logic control component 1106. In another example, if theduty cycle of the dimming signal 1128 is determined to be smaller than athreshold, the system controller 302 is configured to change the signal378 to open (e.g., to turn off) the switch 352 in order to turn off thesystem 300. In yet another example, the comparator 1115 receives thecurrent sensing signal 388 at the terminal 320 (e.g., terminal CS) and athreshold signal 1131 and outputs a comparison signal 1119 (e.g., thesignal 733) to the logic control component 1106. In yet another example,the comparator 1102 receives the signal 386 and a threshold signal 1122to detect whether the demagnetization process has completed. In yetanother example, if the demagnetization process is determined to becompleted, the comparator 1102 outputs a signal 1124 (e.g., the signal724) to the logic control component 1106 which outputs a signal 1130 tothe gate drive component 1108.

FIG. 10 is a simplified diagram showing certain components of the systemcontroller 302 as part of the system 300 as shown in FIG. 9(a), FIG.9(b), and/or FIG. 9(c) according to some embodiments of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 10, the system controller includes a comparator 1904, a detectioncomponent 1911, and a logic control and gate drive component 1998. Forexample, the comparator 1904 is the same as the comparator 904, thecomparator 1004, or the comparator 1104. In another example, thedetection component 1911 is the same as the detection component 911, thedetection component 1011, or the detection component 1111. In yetanother example, the logic control and gate drive component 1998includes the logic control component 906 and the gate drive component908 as shown in FIG. 9(a), the logic control component 1006 and the gatedrive component 1008 as shown in FIG. 9(b), or the logic controlcomponent 1106 and the gate drive component 1108 as shown in FIG. 9(c).

As shown in FIG. 10, the comparator 1904 compares the signal 379 and athreshold signal 1926 (e.g., the threshold signal 926, the thresholdsignal 1026, or the threshold signal 1126) and outputs a dimming signal1928 (e.g., the dimming signal 928, the dimming signal 1028, or thedimming signal 1128) in some embodiments. For example, the phasedetector 1911 receives the dimming signal 1928 and outputs a signal 1933(e.g., the signal 933, the signal 1033, or the signal 1133) to the logiccontrol and gate drive component 1998. In another example, the logiccontrol and gate drive component 1998 also receives the dimming signal1928, a control signal 1920 (e.g., the signal 920, the signal 1020, orthe signal 1120) and a signal 1924 (e.g., the signal 924, the signal1024, or the signal 1124), and outputs the signal 378. In yet anotherexample, a duty cycle of the dimming signal 1928 represents theconduction angle of the TRIAC dimmer 318. In yet another example, theduty cycle of the dimming signal 1928 can be determined as follows:

$\begin{matrix}{{{duty}\mspace{14mu}{cycle}} = {{\frac{T_{on}}{T_{on} + T_{off}}\mspace{20mu}{duty}\mspace{14mu}{cycle}} = \frac{T_{on}}{T_{on} + T_{off}}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$where T_(on) represents a time period when the dimming signal 1928 to beat the logic high level, and T_(off) represents a time period when thedimming signal 1928 to be at the logic low level. For example, T_(on)corresponds to the duration of the on period of the TRIAC dimmer 318 andT_(off) corresponds to the duration of the off period of the TRIACdimmer 318.

According to certain embodiments, the detection component 1911determines the duty cycle of the dimming signal 1928, and outputs thesignal 1933 at the logic low level if the duty cycle of the dimmingsignal 1928 is larger than a threshold. For example, if the signal 1933is at the logic low level and the dimming signal 1928 is at the logichigh level, the logic control and gate drive component 1998 changes, inresponse to the signal 1920, the signal 378 in order to close (e.g., toturn on) or open (e.g., to turn off) the switch 352 corresponding to amodulation frequency, so long as the signal 1924 remains at the logichigh level. In one embodiment, the modulation frequency is equal to 1divided by a corresponding modulation period.

In another example, if the signal 1933 is at the logic low level and thedimming signal 1928 is also at the logic low level, the logic controland gate drive component 1998 affects the signal 378 in order to keepthe switch 352 closed (e.g., on) for a first period of time so long asthe signal 1924 remains at the logic high level. In one embodiment, thefirst period of time is equal to or larger than the modulation period.In another embodiment, the first period of time is larger than themodulation period. In yet another embodiment, the first period of timeis equal to, in duration, the off period of the TRIAC dimmer 318.

According to some embodiments, the detection component 1911 determinesthe duty cycle of the dimming signal 1928, and outputs the signal 1933at the logic high level if the duty cycle of the dimming signal 1928 issmaller than the threshold. For example, if the signal 1933 is at thelogic high level, the logic control and gate drive component 1998affects the signal 378 in order to keep the switch 352 open (e.g., off)for a second period of time until the system 300 is turned off. In oneembodiment, the second period of time is equal to or larger than themodulation period. In another embodiment, the second period of time islarger than the modulation period.

FIG. 11 is a simplified diagram showing certain components of thedetection component 1911 as part of the system controller 302 as shownin FIG. 10 according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The detection component1911 includes current sources 1202 and 1204, transistors 1206 and 1208,a comparator 1210, an amplifier 1212, a D flip flop component 1214, aflip flop component 1216, a delay component 1218, a pulse generator1220, a capacitor 1222, and a switch 1224. For example, the detectioncomponent 1911 is the same as the detection component 911, the detectioncomponent 1011, or the detection component 1111. In another example, thetransistor 1206 is a P-channel field effect transistor. In yet anotherexample, the transistor 1208 is an N-channel field effect transistor.

According to one embodiment, at the beginning of a dimming periodassociated with the TRIAC dimmer 318, the voltage on the capacitor 1222is set to be approximately a predetermined threshold signal 1234 (e.g.,V₀). For example, the signal 1234 is an initial voltage at the capacitor1222 at the beginning of an off period of the TRIAC dimmer 318. Inanother example, during the off period of the TRIAC dimmer 318, thedimming signal 1928 is at a logic low level. In yet another example, inresponse the transistor 1206 is turned on to conduct the current 1230(e.g., I_(c)) associated with the current source 1202 and the transistor1208 is turned off. In yet another example, the capacitor 1222 ischarged by the current 1230 (e.g., I_(c)). In yet another example, thevoltage signal 1228 increases in magnitude (e.g., linearly ornon-linearly). Thus, at the end of the off period of the TRIAC dimmer318, a voltage signal 1228 generated at the capacitor 1222 is determinedas follows, in some embodiments:

$\begin{matrix}{V_{{ramp}\; 1} = {{V_{0} + {\frac{I_{c} \times T_{off}}{C_{1}}\mspace{14mu} V_{{ramp}\; 1}}} = {V_{0} + \frac{I_{c} \times T_{off}}{C_{1}}}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$where V_(ramp1) represents the voltage signal 1228 at the end of the offperiod of the TRIAC dimmer 318, V₀ represents the predeterminedthreshold signal 1234, I_(c) represents the current 1230, and C₁represents the capacitance of the capacitor 1222.

For example, during the on period of the TRIAC dimmer 318, the dimmingsignal 1928 is at a logic high level. In another example, in responsethe transistor 1208 is turned on to conduct the current 1232 (e.g.,I_(d)) associated with the current source 1204 and the transistor 1206is turned off. In yet another example, the capacitor 1222 is discharged,and the voltage signal 1228 decreases in magnitude (e.g., linearly ornon-linearly). Thus, at the end of the on period of the TRIAC dimmer318, the voltage signal 1228 generated at the capacitor 1222 isdetermined as follows, in certain embodiments:

$\begin{matrix}{V_{{ramp}\; 2} = {{V_{{ramp}\; 1} - {\frac{I_{d} \times T_{on}}{C_{1}}\mspace{14mu} V_{{ramp}\; 2}}} = {V_{{ramp}\; 1} - \frac{I_{d} \times T_{on}}{C_{1}}}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$where V_(ramp2) represents the voltage signal 1228 at the end of the onperiod of the TRIAC dimmer 318 and I_(d) represents the current 1232.

Combining Equation (1) and Equation (2), the voltage signal 1228 at theend of the on period of the TRIAC dimmer 318 is determined as follows:

$\begin{matrix}{V_{{ramp}\; 2} = {V_{0} + \frac{I_{c} \times T_{off}}{C_{1}} - \frac{I_{d} \times T_{on}}{C_{1}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

According to another embodiment, the amplifier 1212 receives thethreshold signal 1234 (e.g., V₀) at a non-inverting terminal, and aninverting terminal and an output terminal of the amplifier 1212 areconnected. For example, the amplifier 1212 outputs a signal 1239 whichis approximately equal to the threshold signal 1234 in magnitude. At theend of the on period of the TRIAC dimmer 318, the comparator 1210compares the voltage signal 1228 and the signal 1239 in someembodiments. The following equation is derived from Equation (3),

$\begin{matrix}{{V_{{ramp}\; 2} - V_{0}} = {{\frac{I_{c} \times T_{off}}{C_{1}} - {\frac{I_{d} \times T_{on}}{C_{1}}\mspace{14mu} V_{{ramp}\; 2}} - V_{0}} = {\frac{I_{c} \times T_{off}}{C_{1}} - \frac{I_{d} \times T_{on}}{C_{1}}}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

As shown in Equation (4), if I_(c), I_(d), T_(on) and T_(off) satisfythe following equation, V_(ramp2)=V₀.

$\begin{matrix}{\frac{T_{on}}{T_{off}} = {{\frac{I_{c}}{I_{d}}\mspace{14mu}\frac{T_{on}}{T_{off}}} = \frac{I_{c}}{I_{d}}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

Equation (6) can be transformed mathematically into the followingequation:

$\begin{matrix}{\frac{T_{on}}{T_{on} + T_{off}} = {{\frac{I_{c}}{I_{c} + I_{d}}\mspace{14mu}\frac{T_{on}}{T_{on} + T_{off}}} = \frac{I_{c}}{I_{c} + I_{d}}}} & \left( {{Equation}\mspace{14mu} 7} \right)\end{matrix}$

Thus, a turn-off threshold for the duty cycle of the dimming signal 1928can be determined if the ratio of I_(c) and I_(d) is predefined in someembodiments. For example, if at the end of the on period of the TRIACdimmer 318, the voltage signal 1228 is smaller than the threshold signal1234 in magnitude, the duty cycle of the dimming signal 1928 is largerthan the turn-off threshold and the system controller 302 does not turnoff the system 300. On the other hand, if at the end of the on period ofthe TRIAC dimmer 318, the voltage signal 1228 is larger than thethreshold signal 1234 in magnitude, the duty cycle of the dimming signal1928 is smaller than the turn-off threshold and the system controller302 turns off the system 300.

According to another embodiment, the delay component 1218 receives thedimming signal 1928 and generates a signal 1236 which is received by thepulse generator 1220 and the D flip flop component 1214. For example,the pulse generator 1220 outputs a signal 1238 (e.g., signal Rst) andthe switch 1224 is closed (e.g., turned on) or opened (e.g., turned off)in response to the signal 1238. In another example, the signal 1238includes a pulse at the end of the dimming period, and the switch 1224is closed (e.g., turned on) in response to the pulse to reset thevoltage signal 1228 (e.g., V_(ramp)) to the threshold signal 1234 (e.g.,V₀). In yet another example, the comparator 1210 generates an outputsignal 1240 to the D flip flop component 1214 which also receives thedimming signal 1928 and outputs a signal 1242. In yet another example,the flip flop component 1216 receives the signal 1242 and a signal 1250and outputs the signal 1933. In yet another example, if the signal 1933is at a logic low level, the system controller 302 operates normally,and if the signal 1933 is at a logic high level, the system controller302 changes the signal 378 in order to keep the switch 352 open (e.g.,off) until the system 300 is turned off.

FIG. 12(a) shows simplified timing diagrams for the detection component1911 as part of the system controller 302 for the system 300 if thediming signal 1928 has a large duty cycle, and FIG. 12(b) showssimplified timing diagrams for the detection component 1911 as part ofthe system controller 302 for the system 300 if the dimming signal 1928has a small duty cycle according to some embodiments of the presentinvention. These diagrams are merely examples, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications.

As shown in FIG. 12(a), the waveform 1302 represents the dimming signal1928 as a function of time, the waveform 1304 represents the voltagesignal 1228 as a function of time, the waveform 1306 represents theoutput signal 1240 as a function of time, and the waveform 1308represents the signal 1236 as a function of time. In addition, thewaveform 1310 represents the signal 1238 as a function of time, thewaveform 1312 represents the signal 1242 as a function of time, thewaveform 1314 represents the signal 1250 as a function of time, and thewaveform 1316 represents the signal 1933 as a function of time.

Three time periods are shown in FIG. 12(a), an on time period T_(on2),an off time period T_(off2), and a delay time period T_(d1). The timeperiod T_(on2) starts at time t₄ and ends at time t₆, the time periodT_(off2) starts at the time t₆ and ends at time t₉, and the delay timeperiod T_(d1) starts at the time t₆ and ends at time t₇. For example,t₃≤t₄≤t₅≤t₆≤t₇≤t₈≤t₉≤t₁₀.

As shown in FIG. 12(a), when the duty cycle of the dimming signal 1928is larger than a turn-off threshold, the detection component 1911outputs the signal 1933 at a logic low level (e.g., 0 as shown by thewaveform 1316) in some embodiments. For example, at t₃, the signal 1250changes from a logic low level to a logic high level which indicates thestart of the operating cycle. In another example, the dimming signal1928 keeps at the logic low level during the time period between t₃ andt₄ (e.g., as shown by the waveform 1302). In yet another example, thetransistor 1206 is turned on to conduct the current 1230 (e.g., I_(c))and the transistor 1208 is turned off. In yet another example, inresponse the capacitor 1222 is charged in response to the current 1230and the voltage signal 1228 increases in magnitude (e.g., to a magnitude1320 at t₄ as shown by the waveform 1304).

According to one embodiment, at the beginning of the on time period(e.g., t₄), the dimming signal 1928 changes from the logic low level toa logic high level (e.g., as shown by the waveform 1302). For example,the delay component 1218 changes the signal 1236 from the logic lowlevel to the logic high level (e.g., at t₄ as shown by the waveform1308). In another example, the transistor 1208 is turned on to conductthe current 1232 (e.g., I_(d)) and the transistor 1206 is turned off. Inyet another example, the capacitor 1222 begins to be discharged inresponse. In yet another example, during the on time period, the voltagesignal 1228 decreases in magnitude (e.g., to a magnitude 1322 at t₆ asshown by the waveform 1304). In yet another example, when the voltagesignal 1228 becomes smaller than the threshold signal 1234 (e.g., V₀),the comparator 1210 changes the output signal 1240 from the logic highlevel to the logic low level (e.g., at t₅ as shown by the waveform1306). In yet another example, during the on time period, the signal1933 remains at the logic low level (e.g., as shown by the waveform1316) and the system 300 operates normally.

According to another embodiment, at the beginning of the off time period(e.g., t₆), the dimming signal 1928 changes from the logic high level tothe logic low level (e.g., as shown by the waveform 1301). For example,after a delay (e.g., T_(d1)), the delay component 1218 changes thesignal 1236 from the logic high level to the logic low level (e.g., att₇ as shown by the waveform 1308), so that the D flip flop component1214 which receives the signal 1236 as the reset signal is notimmediately reset when the falling edge of the dimming signal 1928arrives. In another example, upon the falling edge of the signal 1236(e.g., at t₇), the pulse generator 1220 generates a pulse in the signal1238 (e.g., as shown by the waveform 1310). In yet another example, inresponse to the pulse in the signal 1238, the switch 1224 is closed(e.g., turned on) and the voltage signal 1228 is changed to becomeapproximately equal to the output signal 1239 of the amplifier 1212 inmagnitude (e.g., the magnitude 1318 as shown by the waveform 1304).

According to yet another embodiment, during the off time period (e.g.,between t₈ and t₉), the dimming signal 1928 keeps at the logic low level(e.g., as shown by the waveform 1302). In yet another example, thetransistor 1206 is turned on to conduct the current 1230 (e.g., I_(c))and the transistor 1208 is turned off. In yet another example, inresponse the capacitor 1222 is charged in response to the current 1230and the voltage signal 1228 increases in magnitude (e.g., as shown bythe waveform 1304). In yet another example, during the off time period,the signal 1933 remains at the logic low level (e.g., as shown by thewaveform 1316) and the system 300 operates normally.

As shown in FIG. 12(b), the waveform 1402 represents the dimming signal1928 as a function of time, the waveform 1404 represents the voltagesignal 1228 as a function of time, the waveform 1406 represents theoutput signal 1240 as a function of time, and the waveform 1408represents the signal 1236 as a function of time. In addition, thewaveform 1410 represents the signal 1238 as a function of time, thewaveform 1412 represents the signal 1242 as a function of time, thewaveform 1414 represents the signal 1250 as a function of time, and thewaveform 1416 represents the signal 1933 as a function of time.

Two time periods are shown in FIG. 12(b), an on time period T_(on3) andan off time period T_(off3). The time period T_(on3) starts at time t₁₂and ends at time t₁₃ and the time period T_(off3) starts at the time t₁₃and ends at time t₁₆. For example, t₁₁≤t₁₂≤t₁₃≤t₁₄≤t₁₅≤t₁₆≤t₁₇.

As shown in FIG. 12(b), when the duty cycle of the dimming signal 1928is smaller than a turn-off threshold, the detection component 1911changes the signal 1933 from a logic low level to a logic high level(e.g., as shown by the waveform 1416) in some embodiments. For example,at t₁₁, the signal 1250 changes from a logic low level to a logic highlevel which indicates the start of the operating cycle. In anotherexample, the dimming signal 1928 keeps at the logic low level during thetime period between t₁₁ and t₁₂ (e.g., as shown by the waveform 1402).In yet another example, the transistor 1206 is turned on to conduct thecurrent 1230 (e.g., I_(c)) and the transistor 1208 is turned off. In yetanother example, in response the capacitor 1222 is charged in responseto the current 1230 and the voltage signal 1228 increases in magnitude(e.g., to a magnitude 1420 at t₁₂ as shown by the waveform 1404).

According to one embodiment, at the beginning of the on time period(e.g., t₁₂), the dimming signal 1928 changes from the logic low level toa logic high level (e.g., as shown by the waveform 1402). For example,the delay component 1218 changes the signal 1236 from the logic lowlevel to the logic high level (e.g., at t₁₂ as shown by the waveform1408). In another example, the transistor 1208 is turned on to conductthe current 1232 (e.g., I_(d)) and the transistor 1206 is turned off. Inyet another example, the capacitor 1222 begins to be discharged inresponse. In yet another example, during the on time period, the voltagesignal 1228 decreases in magnitude (e.g., to a magnitude 1422 at t₁₃),but keeps larger than the threshold signal 1234 in magnitude (e.g., asshown by the waveform 1404). In yet another example, the comparator 1210keeps the output signal 1240 at the logic high level (e.g., as shown bythe waveform 1406). In yet another example, during the on time period,the signal 1933 remains at the logic low level (e.g., as shown by thewaveform 1416) and the system 300 operates normally.

According to another embodiment, at the beginning of the off time period(e.g., t₁₃), the dimming signal 1928 changes from the logic high levelto the logic low level (e.g., as shown by the waveform 1402). Forexample, after a delay (e.g., T_(d2)), the delay component 1218 changesthe signal 1236 from the logic high level to the logic low level (e.g.,at t₁₄ as shown by the waveform 1408). In another example, upon thefalling edge of the signal 1236 (e.g., at t₁₄), the pulse generator 1220generates a pulse in the signal 1238 (e.g., as shown by the waveform1410). In yet another example, the D flip flop component that receivesthe dimming signal 1928 generates a pulse in the signal 1242 in responseto the falling edge of the dimming signal 1928 (e.g., as shown by thewaveform 1412). In yet another example, the flip flop component 1216changes the signal 1933 from the logic low level to the logic high levelin response to the pulse in the signal 1242 (e.g., as shown by thewaveform 1416). In yet another example, the system controller 302changes the signal 378 in order to keep the switch 352 open (e.g., off)until the system 300 is turned off.

As shown in FIG. 12(a) and FIG. 12(b), at the end of the off period ofthe TRIAC dimmer 318 (e.g., at t₉ as shown in FIG. 12(a) or at t₁₆ asshown in FIG. 12(b)), the voltage signal 1228 generated at the capacitor1222 can be determined as follows, in some embodiments:

$\begin{matrix}{V_{{ramp}\; 1} = {V_{0} + \frac{I_{c} \times \left( {T_{off} - T_{d} - T_{pulse}} \right)}{C_{1}}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$where V_(ramp1) represents the voltage signal 1228 at the end of the offperiod of the TRIAC dimmer 318, V₀ represents the predeterminedthreshold signal 1234, I_(c) represents the current 1230, and C₁represents the capacitance of the capacitor 1222. In addition, T_(off)represents the duration of the off period of the TRIAC dimmer 318, T_(d)represents the delay between a falling edge of the dimming signal 1928and a falling edge of the signal 1236 during a same dimming period ofthe TRIAC dimmer 318 (e.g., T_(d1) in FIG. 12(a) and T_(d2) in FIG.12(b)), and T_(pulse) represents a pulse width in the signal 1238.

For example, T_(off)>>T_(d)+T_(pulse), and thus

$\begin{matrix}{V_{{ramp}\; 1} \approx {V_{0} + \frac{I_{c} \times T_{off}}{C_{1}}}} & \left( {{Equation}\mspace{14mu} 9} \right)\end{matrix}$At the end of the on period of the TRIAC dimmer 318 (e.g., at t₁₀ asshown in FIG. 12(a) or at t₁₇ as shown in FIG. 12(b)), the voltagesignal 1228 generated at the capacitor 1222 is determined as follows, incertain embodiments:

$\begin{matrix}{V_{{ramp}\; 2} \approx {V_{{ramp}\; 1} - \frac{I_{d} \times T_{on}}{C_{1}}}} & \left( {{Equation}\mspace{14mu} 10} \right)\end{matrix}$where V_(ramp2) represents the voltage signal 1228 at the end of the onperiod of the TRIAC dimmer 318 and I_(d) represents the current 1232.

Combining Equation (9) and Equation (10) yields the following equation:

$\begin{matrix}{V_{{ramp}\; 2} \approx {V_{0} + \frac{I_{c} \times T_{off}}{C_{1}} - \frac{I_{d} \times T_{on}}{C_{1}}}} & \left( {{Equation}\mspace{14mu} 11} \right)\end{matrix}$Thus,

$\begin{matrix}{{V_{{ramp}\; 2} - V_{0}} \approx {\frac{I_{c} \times T_{off}}{C_{1}} - \frac{I_{d} \times T_{on}}{C_{1}}}} & \left( {{Equation}\mspace{14mu} 12} \right)\end{matrix}$

As shown in Equation (12), if I_(c), I_(d), T_(on) and T_(off) satisfyEquation 6, V_(ramp2)≅≈V₀. Thus, a turn-off threshold for the duty cycleof the dimming signal 1928 can be approximately determined according toEquation 7 if the ratio of I_(c) and I_(d) is predefined, in someembodiments.

According to another embodiment, a system for dimming control of one ormore light emitting diodes includes one or more signal processingcomponents configured to receive a first signal associated with a TRIACdimmer, process information associated with the first signal, determinewhether the TRIAC dimmer is in a first condition or a second condition,generate a second signal based on at least information associated withthe first signal, and send the second signal to a switch. The one ormore signal processing components are further configured to, if theTRIAC dimmer is determined to be in the first condition, generate thesecond signal to cause the switch to be opened and closed correspondingto a modulation frequency, and if the TRIAC dimmer is determined to bein the second condition, generate the second signal to cause the switchto remain closed for a first period of time until at least the TRIACdimmer changes from the second condition to the first condition. Forexample, the system is implemented according to FIG. 3, FIG. 4, FIG. 5,FIG. 6, FIG. 7, FIG. 9(a), FIG. 9(b), FIG. 9(c), FIG. 10, FIG. 11, FIG.12(a) and/or FIG. 12(b).

For example, the one or more signal processing components are furtherconfigured to determine whether the TRIAC dimmer is in a thirdcondition; and if the TRIAC dimmer is determined to be in the thirdcondition, generate the second signal to cause the switch to remain openfor a second period of time. In another example, the first period oftime is larger than a modulation period corresponding to the modulationfrequency. In yet another example, the second period of time is largerthan a modulation period corresponding to the modulation frequency. Inyet another example, the one or more signal processing components arefurther configured to generate a third signal based on at leastinformation associated with the first signal, process informationassociated with the third signal, and generate the second signal basedon at least information associated with the third signal. In yet anotherexample, the one or more signal processing components are furtherconfigured to, if a duty cycle of the second signal is larger than athreshold value and if the first signal is larger than a thresholdsignal in magnitude, determine the TRIAC dimmer to be in the firstcondition. In yet another example, the one or more signal processingcomponents are further configured to, if a duty cycle of the secondsignal is larger than the threshold value and if the first signal issmaller than the threshold signal in magnitude, determine the TRIACdimmer to be in the second condition. In yet another example, whereinthe one or more signal processing components are further configured to,if a duty cycle of the second signal is smaller than the thresholdvalue, determine the TRIAC dimmer to be in the third condition. In yetanother example, the one or more signal processing components arefurther configured to process information associated with the firstsignal and a threshold signal, determine the TRIAC dimmer to be in thefirst condition if the first signal is larger than the threshold signalin magnitude, and determine the TRIAC dimmer to be in the secondcondition if the first signal is smaller than the threshold signal inmagnitude.

For example, the first condition corresponds to an on condition for theTRIAC dimmer, and the second condition corresponds to an off conditionfor the TRIAC dimmer. In another example, the one or more signalprocessing components includes, a first comparator configured to receivea first threshold signal and the first signal and generate a comparisonsignal based on at least information associated with the first thresholdsignal and the first signal, and a driving component configured toreceive the comparison signal, generate the second signal based on atleast information associated with the comparison signal, and output thesecond signal to the switch. In yet another example, the one or moresignal processing components further includes, a modulation componentconfigured to receive a current sensing signal associated with a primarycurrent flowing through a primary winding of a transformer and a thirdsignal associated with the first signal and output a modulation signalto the driving component based on at least information associated withthe current sensing signal and the third signal, the transformer furtherincluding a secondary winding and an auxiliary winding. The modulationcomponent is further configured to, if the current sensing signal islarger than the third signal in magnitude, generate the modulationsignal at a first logic level to cause the switch to be opened, and ifthe current sensing signal is smaller than the third signal inmagnitude, generate the modulation signal at a second logic level tocause the switch to be closed. In yet another example, the one or moresignal processing components further includes, a multiplexer configuredto receive the first signal and a fourth signal and generate a fifthsignal based on at least information associated with the first signaland the fourth signal, and an offset component configured to receive thefifth signal and output the third signal by adding a predeterminedoffset to the fifth signal to keep the third signal no smaller than thecurrent sensing signal in magnitude when the TRIAC dimmer is in thesecond condition.

As an example, the one or more signal processing components furtherincludes, a second comparator configured to receive the current sensingsignal and a second threshold signal and output a fourth signal to thedriving component based on at least information associated with thecurrent sensing signal and the second threshold signal. The secondcomparator is further configured to, if the current sensing signal issmaller than the second threshold signal in magnitude, generate thefourth signal at a third logic level to cause the switch to be closed.In another example, the one or more signal processing components furtherincludes a multiplexer configured to receive the first signal and afourth signal and output the third signal to the modulation componentbased on at least information associated with the first signal and thefourth signal. In yet another example, the one or more signal processingcomponents further includes a current regulation component configured toreceive the current sensing signal and output a processed signal to themultiplexer based on at least information associated with the currentsensing signal. In yet another example, the one or more signalprocessing components further includes a second comparator configured toreceive a fourth signal associated with the auxiliary winding and asecond threshold signal and output a fifth signal to the drivingcomponent based on at least information associated with the fourthsignal and the second threshold signal, the fifth signal indicatingwhether a demagnetization process associated with the transformer hascompleted.

According to another embodiment, a system for dimming control of one ormore light emitting diodes includes a first comparator and a drivingcomponent. The first comparator is configured to receive a firstthreshold signal and an input signal associated with a TRIAC dimmer andgenerate a comparison signal based on at least information associatedwith the first threshold signal and the input signal. The drivingcomponent is configured to receive the comparison signal, generate anoutput signal based on at least information associated with thecomparison signal, and send the output signal to a switch. The firstcomparator is further configured to generate the comparison signal at afirst logic level if the input signal is larger than the first thresholdsignal in magnitude and generate the comparison signal at a second logiclevel if the input signal is smaller than the first threshold signal inmagnitude. The driving component is further configured to generate theoutput signal and cause the switch to remain closed for a period of timeuntil at least the comparison signal changes from the second logic levelto the first logic level. For example, the system is implementedaccording to at least FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 9(a),FIG. 9(b), FIG. 9(c), FIG. 10, FIG. 12(a) and/or FIG. 12(b).

For example, the driving component is further configured to, if thecomparison signal is at the first logic level, generate the outputsignal to cause the switch to be opened and closed corresponding to amodulation frequency. In another example, the period of time is largerthan a modulation period corresponding to the modulation frequency. Inyet another example, the system further includes a modulation componentconfigured to receive a current sensing signal associated with a primarycurrent flowing through a primary winding of a transformer and a thirdsignal associated with the input signal and output a modulation signalto the driving component based on at least information associated withthe current sensing signal and the third signal, the transformer furtherincluding a secondary winding and an auxiliary winding. The modulationcomponent is further configured to, if the current sensing signal islarger than the third signal in magnitude, generate the modulationsignal at a third logic level to cause the switch to be opened, and ifthe current sensing signal is smaller than the third signal inmagnitude, generate the modulation signal at a fourth logic level tocause the switch to be closed. In yet another example, the systemfurther includes, a multiplexer configured to receive the input signaland a fourth signal and generate a fifth signal based on at leastinformation associated with the input signal and the fourth signal, andan offset component configured to receive the fifth signal and outputthe third signal by adding a predetermined offset to the fifth signal tocause the third signal to be larger than the current sensing signal inmagnitude when the input signal is smaller than the first thresholdsignal in magnitude.

As an example, the system further includes a second comparatorconfigured to receive the current sensing signal and a second thresholdsignal and output a fourth signal to the driving component based on atleast information associated with the current sensing signal and thesecond threshold signal. The second comparator is further configured to,if the current sensing signal is smaller than the second thresholdsignal in magnitude, generate the fourth signal at a fifth logic levelto cause the switch to be closed. In another example, the system furtherincludes a multiplexer configured to receive the input signal and afourth signal and output the third signal to the modulation componentbased on at least information associated with the input signal and thefourth signal. In yet another example, the system further includes acurrent regulation component configured to receive the current sensingsignal and output a processed signal to the multiplexer based on atleast information associated with the current sensing signal. In yetanother example, the system further includes a second comparatorconfigured to receive a fourth signal associated with the auxiliarywinding and a second threshold signal and output a fifth signal to thedriving component based on at least information associated with thefourth signal and the second threshold signal, the fifth signalindicating whether a demagnetization process associated with thetransformer has completed.

According to yet another embodiment, a system for dimming control of oneor more light emitting diodes includes a first comparator, a detectioncomponent, and a driving component. The first comparator is configuredto receive a first threshold signal and a first signal associated with aTRIAC dimmer and generate a first comparison signal based on at leastinformation associated with the first threshold signal and the firstsignal. The detection component is configured to receive the firstcomparison signal, determine a duty cycle of the first comparisonsignal, process information associated with the duty cycle and athreshold value, and generate a detection signal based on at leastinformation associated with the first comparison signal. The drivingcomponent is configured to receive the detection signal, generate asecond signal based on at least information associated with thedetection signal, and output the second signal to a switch. The firstcomparator is further configured to generate the first comparison signalat a first logic level if the first signal is larger than the thresholdsignal in magnitude and generate the first comparison signal at a secondlogic level if the first signal is smaller than the threshold signal inmagnitude. The detection component is further configured to generate thedetection signal at a third logic level if the duty cycle of the firstcomparison signal is larger than the threshold value in magnitude andgenerate the detection signal at a fourth logic level if the duty cycleof the first comparison signal is smaller than the threshold value inmagnitude. The driving component is further configured to, if thedetection signal is at the fourth logic level, generate the secondsignal to cause the switch to remain open for a first period of time.For example, the system is implemented according to at least FIG. 3,FIG. 9(a), FIG. 9(b), FIG. 9(c), FIG. 10, FIG. 11, FIG. 12(a) and/orFIG. 12(b).

For example, the first comparator is further configured to output thecomparison signal to the driving component, and the driving component isfurther configured to generate the second signal to cause the switch toremain closed for a second period of time until at least the comparisonsignal changes from the first logic level to the second logic level. Inanother example, the driving component is further configured to, if thecomparison signal is at the first logic level and the detection signalis at the third logic level, generate the second signal to cause theswitch to be opened and closed corresponding to a modulation frequency.In yet another example, the first period of time is larger than amodulation period corresponding to the modulation frequency. In yetanother example, the second period of time is larger than a modulationperiod corresponding to the modulation frequency. In yet anotherexample, the detection component includes, a voltage generatorconfigured to receive the first comparison signal and generate a thirdsignal based on at least information associated with the firstcomparison signal, a second comparator configured to receive the thirdsignal and a threshold signal and generate a second comparison signalbased on at least information associated with the third signal and thethreshold signal, and a signal processor configured to receive the firstcomparison signal and the second comparison signal and generate anoutput signal based on at least information associated with the firstcomparison signal and the second comparison signal.

According to yet another embodiment, a system for detecting a duty cycleof a signal includes a voltage generator, a comparator, and a signalgenerator. The voltage generator is configured to receive an inputsignal and generate a first voltage signal based on at least informationassociated with the input signal. The comparator is configured toreceive the first voltage signal and a threshold signal and generate acomparison signal based on at least information associated with thefirst voltage signal and the threshold signal. The signal processor isconfigured to receive the comparison signal and the input signal andgenerate an output signal based on at least information associated withthe comparison signal and the input signal. The comparator is furtherconfigured to, if the first voltage signal is larger than the thresholdsignal in magnitude, generate the comparison signal at a first logiclevel, and if the first voltage signal is smaller than the thresholdsignal in magnitude, generate the comparison signal at a second logiclevel. The signal processor is further configured to, if a duty cycle ofthe input signal is larger than a threshold value, generate the outputsignal at a third logic level, and if the duty cycle of the input signalis smaller than the threshold value, generate the output signal at afourth logic level. The signal processor is further configured to, ifthe input signal changes from a fifth logic level to a sixth logic leveland if the comparison signal is at the first logic level, change theoutput signal from the third logic level to the fourth logic level. Forexample, the system is implemented according to at least FIG. 3, FIG.9(a), FIG. 9(b), FIG. 9(c), FIG. 10, FIG. 11, FIG. 12(a) and/or FIG.12(b).

For example, the voltage generator includes, a first current sourceconfigured to provide a first current, a second current sourceconfigured to provide a second current, a first transistor configured toconduct the first current if the input signal is at the sixth logiclevel, a second transistor configured to conduct the second current ifthe input signal is at the fifth logic level; and a capacitor configuredto, if the input signal is at the sixth logic level, be charged by thefirst current flowing through the first transistor, and if the inputsignal is at the fifth logic level, be discharged by the second currentflowing through the second transistor. In another example, the systemfurther includes a switch coupled between a first input terminal of thecomparator and a second input terminal of the comparator, the comparatorfurther configured to receive the first voltage signal at the firstinput terminal and receive the threshold signal at the second inputterminal. The switch is configured, if the input signal changes from thefifth logic level to the sixth logic level, to be closed after apredetermined delay. In yet another example, the system further includesa signal generator configured to receive the input signal, generate afirst signal based on at least information associated with the inputsignal, and send the first signal to the switch. The signal generator isfurther configured to, if the input signal changes from the fifth logiclevel to the sixth logic level, change the first signal from a seventhlogic level to an eighth logic level after the determined delay. In yetanother example, the signal generator is further configured to, if theinput signal changes from the fifth logic level to the sixth logiclevel, after the first signal is changed from the seventh logic level tothe eighth logic level, change the first signal back to the seventhlogic level from the eighth logic level to form a signal pulse. In yetanother example, the switch is further configured to, if the firstsignal is at the seventh logic level, be opened, and if the first signalis at the eighth logic level, be closed.

In one embodiment, a method for dimming control of one or more lightemitting diodes includes, receiving a first signal associated with aTRIAC dimmer, processing information associated with the first signal,and determining whether the TRIAC dimmer is in a first condition or asecond condition based on at least information associated with the firstsignal. The method further includes generating a second signal based onat least information associated with the first signal, and outputtingthe second signal to a switch. The process for generating a secondsignal based on at least information associated with the first signalincludes, if the TRIAC dimmer is determined to be in the firstcondition, generating the second signal to cause the switch to be openedand closed corresponding to a modulation frequency, and if the TRIACdimmer is determined to be in the second condition, generating thesecond signal to cause the switch to remain closed for a first period oftime until at least the TRIAC dimmer changes from the second conditionto the first condition. For example, the method is implemented accordingto FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 9(a), FIG. 9(b), FIG.9(c), FIG. 10, FIG. 11, FIG. 12(a) and/or FIG. 12(b).

For example, the method further includes determining whether the TRIACdimmer is in a third condition. The process for generating a secondsignal based on at least information associated with the first signalfurther includes, if the TRIAC dimmer is determined to be in the thirdcondition, generating the second signal to cause the switch to remainopen for a second period of time. In another example, the first periodof time is larger than a modulation period corresponding to themodulation frequency. In yet another example, the second period of timeis larger than a modulation period corresponding to the modulationfrequency. In yet another example, the method further includesgenerating a third signal based on at least information associated withthe first signal, processing information associated with the thirdsignal, and generating the second signal based on at least informationassociated with the third signal. In yet another example, the processfor determining whether the TRIAC dimmer is in a first condition or asecond condition includes, if a duty cycle of the second signal islarger than a threshold value and if the first signal is larger than athreshold signal in magnitude, determining the TRIAC dimmer to be in thefirst condition. In yet another example, the process for determiningwhether the TRIAC dimmer is in a first condition or a second conditionincludes, if a duty cycle of the second signal is larger than thethreshold value and if the first signal is smaller than the thresholdsignal in magnitude, determining the TRIAC dimmer to be in the secondcondition. In yet another example, the process for determining whetherthe TRIAC dimmer is in a third condition includes, if a duty cycle ofthe second signal is smaller than the threshold value, determining theTRIAC dimmer to be in the third condition. In yet another example, themethod further includes receiving a threshold signal, and processinginformation associated with the threshold signal. The process fordetermining whether the TRIAC dimmer is in a first condition or a secondcondition includes, if the first signal is larger than the thresholdsignal in magnitude, determining the TRIAC dimmer to be in the firstcondition, and if the first signal is smaller than the threshold signalin magnitude, determining the TRIAC dimmer to be in the secondcondition.

In another embodiment, a method for dimming control of one or more lightemitting diodes includes, receiving a threshold signal and an inputsignal associated with a TRIAC dimmer, generating a comparison signalbased on at least information associated with the first threshold signaland the input signal, and receiving the comparison signal. The methodfurther includes generating an output signal based on at leastinformation associated with the comparison signal and sending the outputsignal to a switch. The process for generating a comparison signal basedon at least information associated with the first threshold signal andthe input signal includes, if the input signal is larger than the firstthreshold signal in magnitude, generating the comparison signal at afirst logic level, and if the input signal is smaller than the firstthreshold signal in magnitude, generating the comparison signal at asecond logic level. The process for sending the output signal to aswitch includes sending the output signal to cause the switch to remainclosed for a period of time until at least the comparison signal changesfrom the second logic level to the first logic level. For example, themethod is implemented according to at least FIG. 3, FIG. 4, FIG. 5, FIG.6, FIG. 7, FIG. 9(a), FIG. 9(b), FIG. 9(c), FIG. 10, FIG. 12(a) and/orFIG. 12(b).

For example, the process for sending the output signal to a switchincludes, if the comparison signal is at the first logic level, sendingthe output signal to cause the switch to be opened and closedcorresponding to a modulation frequency. In another example, the periodof time is larger than a modulation period corresponding to themodulation frequency.

In yet another embodiment, a method for dimming control of one or morelight emitting diodes includes receiving a threshold signal and an inputsignal associated with a TRIAC dimmer, generating a comparison signalbased on at least information associated with the threshold signal andthe input signal, and receiving the comparison signal. The methodfurther includes determining a duty cycle of the comparison signal,processing information associated with the duty cycle and a thresholdvalue, and generating a detection signal based on at least informationassociated with the comparison signal. In addition, the method includesreceiving the detection signal, generating an output signal based on atleast information associated with the detection signal, and sending theoutput signal to a switch. The process for generating a comparisonsignal based on at least information associated with the thresholdsignal and the input signal includes, if the input signal is larger thanthe threshold signal in magnitude, generating the comparison signal at afirst logic level, and if the input signal is smaller than the thresholdsignal in magnitude, generating the comparison signal at a second logiclevel. The process for generating a detection signal based on at leastinformation associated with the comparison signal includes, if the dutycycle of the comparison signal is larger than the threshold value inmagnitude, generating the detection signal at a third logic level, andif the duty cycle of the comparison signal is smaller than the thresholdvalue in magnitude, generating the detection signal at a fourth logiclevel. The process for generating an output signal based on at leastinformation associated with the detection signal includes if thedetection signal is at the fourth logic level, generating the outputsignal to cause the switch to remain open for a first period of time.For example, the method is implemented according to at least FIG. 3,FIG. 9(a), FIG. 9(b), FIG. 9(c), FIG. 10, FIG. 11, FIG. 12(a) and/orFIG. 12(b).

For example, the process for generating an output signal based on atleast information associated with the detection signal further includes,generating the output signal to cause the switch to remain closed for asecond period of time until at least the comparison signal changes fromthe first logic level to the second logic level. In another example, theprocess for generating an output signal based on at least informationassociated with the detection signal further includes, if the comparisonsignal is at the first logic level and the detection signal is at thethird logic level, generating the output signal to cause the switch tobe opened and closed corresponding to a modulation frequency. In yetanother example, the first period of time is larger than a modulationperiod corresponding to the modulation frequency. In yet anotherexample, the second period of time is larger than a modulation periodcorresponding to the modulation frequency.

In yet another embodiment, a method for detecting a duty cycle of asignal includes receiving an input signal, generating a first voltagesignal based on at least information associated with the input signal,and receiving the first voltage signal and a threshold signal. Themethod further includes generating a comparison signal based on at leastinformation associated with the first voltage signal and the thresholdsignal, receiving the comparison signal and the input signal, andgenerating an output signal based on at least information associatedwith the comparison signal and the input signal. The process forgenerating a comparison signal based on at least information associatedwith the first voltage signal and the threshold signal includes, if thefirst voltage signal is larger than the threshold signal in magnitude,generating the comparison signal at a first logic level, and if thefirst voltage signal is smaller than the threshold signal in magnitude,generating the comparison signal at a second logic level. The processfor generating an output signal based on at least information associatedwith the comparison signal and the input signal includes, if a dutycycle of the input signal is larger than a threshold value, generatingthe output signal at a third logic level, if the duty cycle of the inputsignal is smaller than the threshold value, generating the output signalat a fourth logic level, and if the input signal changes from a fifthlogic level to a sixth logic level and if the comparison signal is atthe first logic level, changing the output signal from the third logiclevel to the fourth logic level. For example, the method is implementedaccording to at least FIG. 3, FIG. 9(a), FIG. 9(b), FIG. 9(c), FIG. 10,FIG. 11, FIG. 12(a) and/or FIG. 12(b).

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system for dimming control of one or more lightemitting diodes, the system comprising: a first comparator configured toreceive a first threshold signal and an input signal associated with aTRIAC dimmer and generate a comparison signal based on at leastinformation associated with the first threshold signal and the inputsignal; a driving component configured to receive the comparison signal,generate an output signal based on at least information associated withthe comparison signal, and send the output signal to a switch; amodulation component configured to receive a current sensing signalassociated with a primary current flowing through a primary winding of atransformer and a third signal associated with the input signal andoutput a modulation signal to the driving component based on at leastinformation associated with the current sensing signal and the thirdsignal, the transformer further including a secondary winding and anauxiliary winding; a multiplexer configured to receive the input signaland a fourth signal and generate a fifth signal based on at leastinformation associated with the input signal and the fourth signal; andan offset component configured to receive the fifth signal and outputthe third signal by adding a predetermined offset to the fifth signal tocause the third signal to be larger than the current sensing signal inmagnitude when the input signal is smaller than the first thresholdsignal in magnitude; wherein: the first comparator is further configuredto generate the comparison signal at a first logic level if the inputsignal is larger than the first threshold signal in magnitude andgenerate the comparison signal at a second logic level if the inputsignal is smaller than the first threshold signal in magnitude; and thedriving component is further configured to generate the output signaland cause the switch to remain closed for a period of time until atleast the comparison signal changes from the second logic level to thefirst logic level; wherein the modulation component is furtherconfigured to: if the current sensing signal is larger than the thirdsignal in magnitude, generate the modulation signal at a third logiclevel to cause the switch to be opened; and if the current sensingsignal is smaller than the third signal in magnitude, generate themodulation signal at a fourth logic level to cause the switch to beclosed.
 2. The system of claim 1 wherein the driving component isfurther configured to, if the comparison signal is at the first logiclevel, generate the output signal to cause the switch to be opened andclosed corresponding to a modulation frequency.
 3. The system of claim 2wherein the period of time is larger than a modulation periodcorresponding to the modulation frequency.
 4. A system for dimmingcontrol of one or more light emitting diodes, the system comprising: afirst comparator configured to receive a first threshold signal and aninput signal associated with a TRIAC dimmer and generate a comparisonsignal based on at least information associated with the first thresholdsignal and the input signal; a driving component configured to receivethe comparison signal, generate an output signal based on at leastinformation associated with the comparison signal, and send the outputsignal to a switch; a modulation component configured to receive acurrent sensing signal associated with a primary current flowing througha primary winding of a transformer and a third signal associated withthe input signal and output a modulation signal to the driving componentbased on at least information associated with the current sensing signaland the third signal, the transformer further including a secondarywinding and an auxiliary winding; and a second comparator configured toreceive the current sensing signal and a second threshold signal andoutput a fourth signal to the driving component based on at leastinformation associated with the current sensing signal and the secondthreshold signal; wherein: the first comparator is further configured togenerate the comparison signal at a first logic level if the inputsignal is larger than the first threshold signal in magnitude andgenerate the comparison signal at a second logic level if the inputsignal is smaller than the first threshold signal in magnitude; and thedriving component is further configured to generate the output signaland cause the switch to remain closed for a period of time until atleast the comparison signal changes from the second logic level to thefirst logic level; wherein the modulation component is furtherconfigured to: if the current sensing signal is larger than the thirdsignal in magnitude, generate the modulation signal at a third logiclevel to cause the switch to be opened; and if the current sensingsignal is smaller than the third signal in magnitude, generate themodulation signal at a fourth logic level to cause the switch to beclosed; wherein the second comparator is further configured to, if thecurrent sensing signal is smaller than the second threshold signal inmagnitude, generate the fourth signal at a fifth logic level to causethe switch to be closed.
 5. A system for dimming control of one or morelight emitting diodes, the system comprising: a first comparatorconfigured to receive a first threshold signal and an input signalassociated with a TRIAC dimmer and generate a comparison signal based onat least information associated with the first threshold signal and theinput signal; a driving component configured to receive the comparisonsignal, generate an output signal based on at least informationassociated with the comparison signal, and send the output signal to aswitch; a modulation component configured to receive a current sensingsignal associated with a primary current flowing through a primarywinding of a transformer and a third signal associated with the inputsignal and output a modulation signal to the driving component based onat least information associated with the current sensing signal and thethird signal, the transformer further including a secondary winding andan auxiliary winding; and a multiplexer configured to receive the inputsignal and a fourth signal and output the third signal to the modulationcomponent based on at least information associated with the input signaland the fourth signal; wherein: the first comparator is furtherconfigured to generate the comparison signal at a first logic level ifthe input signal is larger than the first threshold signal in magnitudeand generate the comparison signal at a second logic level if the inputsignal is smaller than the first threshold signal in magnitude; and thedriving component is further configured to generate the output signaland cause the switch to remain closed for a period of time until atleast the comparison signal changes from the second logic level to thefirst logic level; wherein the modulation component is furtherconfigured to: if the current sensing signal is larger than the thirdsignal in magnitude, generate the modulation signal at a third logiclevel to cause the switch to be opened; and if the current sensingsignal is smaller than the third signal in magnitude, generate themodulation signal at a fourth logic level to cause the switch to beclosed.
 6. The system of claim 5, and further comprising: a currentregulation component configured to receive the current sensing signaland output a processed signal to the multiplexer based on at leastinformation associated with the current sensing signal.
 7. A system fordimming control of one or more light emitting diodes, the systemcomprising: a first comparator configured to receive a first thresholdsignal and an input signal associated with a TRIAC dimmer and generate acomparison signal based on at least information associated with thefirst threshold signal and the input signal; a driving componentconfigured to receive the comparison signal, generate an output signalbased on at least information associated with the comparison signal, andsend the output signal to a switch; a modulation component configured toreceive a current sensing signal associated with a primary currentflowing through a primary winding of a transformer and a third signalassociated with the input signal and output a modulation signal to thedriving component based on at least information associated with thecurrent sensing signal and the third signal, the transformer furtherincluding a secondary winding and an auxiliary winding; and a secondcomparator configured to receive a fourth signal associated with theauxiliary winding and a second threshold signal and output a fifthsignal to the driving component based on at least information associatedwith the fourth signal and the second threshold signal, the fifth signalindicating whether a demagnetization process associated with thetransformer has completed; wherein: the first comparator is furtherconfigured to generate the comparison signal at a first logic level ifthe input signal is larger than the first threshold signal in magnitudeand generate the comparison signal at a second logic level if the inputsignal is smaller than the first threshold signal in magnitude; and thedriving component is further configured to generate the output signaland cause the switch to remain closed for a period of time until atleast the comparison signal changes from the second logic level to thefirst logic level; wherein the modulation component is furtherconfigured to: if the current sensing signal is larger than the thirdsignal in magnitude, generate the modulation signal at a third logiclevel to cause the switch to be opened; and if the current sensingsignal is smaller than the third signal in magnitude, generate themodulation signal at a fourth logic level to cause the switch to beclosed.
 8. A system for dimming control of one or more light emittingdiodes, the system comprising: a first comparator configured to receivea first threshold signal and a first signal associated with a TRIACdimmer and generate a first comparison signal based on at leastinformation associated with the first threshold signal and the firstsignal; a detection component configured to receive the first comparisonsignal, determine a duty cycle of the first comparison signal, processinformation associated with the duty cycle and a threshold value, andgenerate a detection signal based on at least information associatedwith the first comparison signal; and a driving component configured toreceive the detection signal, generate a second signal based on at leastinformation associated with the detection signal, and output the secondsignal to a switch; wherein: the first comparator is further configuredto generate the first comparison signal at a first logic level if thefirst signal is larger than the threshold signal in magnitude andgenerate the first comparison signal at a second logic level if thefirst signal is smaller than the threshold signal in magnitude; thedetection component is further configured to generate the detectionsignal at a third logic level if the duty cycle of the first comparisonsignal is larger than the threshold value in magnitude and generate thedetection signal at a fourth logic level if the duty cycle of the firstcomparison signal is smaller than the threshold value in magnitude; andthe driving component is further configured to, if the detection signalis at the fourth logic level, generate the second signal to cause theswitch to remain open for a first period of time.
 9. The system of claim8 wherein: the first comparator is further configured to output thecomparison signal to the driving component; and the driving component isfurther configured to generate the second signal to cause the switch toremain closed for a second period of time until at least the comparisonsignal changes from the first logic level to the second logic level. 10.The system of claim 9 wherein the driving component is furtherconfigured to, if the comparison signal is at the first logic level andthe detection signal is at the third logic level, generate the secondsignal to cause the switch to be opened and closed corresponding to amodulation frequency.
 11. The system of claim 10 wherein the firstperiod of time is larger than a modulation period corresponding to themodulation frequency.
 12. The system of claim 10 wherein the secondperiod of time is larger than a modulation period corresponding to themodulation frequency.
 13. The system of claim 8 wherein the detectioncomponent includes: a voltage generator configured to receive the firstcomparison signal and generate a third signal based on at leastinformation associated with the first comparison signal; a secondcomparator configured to receive the third signal and a threshold signaland generate a second comparison signal based on at least informationassociated with the third signal and the threshold signal; and a signalprocessor configured to receive the first comparison signal and thesecond comparison signal and generate an output signal based on at leastinformation associated with the first comparison signal and the secondcomparison signal.
 14. A system for detecting a duty cycle of a signal,the system comprising: a voltage generator configured to receive aninput signal and generate a first voltage signal based on at leastinformation associated with the input signal; a comparator configured toreceive the first voltage signal and a threshold signal and generate acomparison signal based on at least information associated with thefirst voltage signal and the threshold signal; and a signal processorconfigured to receive the comparison signal and the input signal andgenerate an output signal based on at least information associated withthe comparison signal and the input signal; wherein the comparator isfurther configured to: if the first voltage signal is larger than thethreshold signal in magnitude, generate the comparison signal at a firstlogic level; if the first voltage signal is smaller than the thresholdsignal in magnitude, generate the comparison signal at a second logiclevel; wherein the signal processor is further configured to: if a dutycycle of the input signal is larger than a threshold value, generate theoutput signal at a third logic level; and if the duty cycle of the inputsignal is smaller than the threshold value, generate the output signalat a fourth logic level; wherein the signal processor is furtherconfigured to, if the input signal changes from a fifth logic level to asixth logic level and if the comparison signal is at the first logiclevel, change the output signal from the third logic level to the fourthlogic level.
 15. The system of claim 14 wherein the voltage generatorincludes: a first current source configured to provide a first current;a second current source configured to provide a second current; a firsttransistor configured to conduct the first current if the input signalis at the sixth logic level; a second transistor configured to conductthe second current if the input signal is at the fifth logic level; anda capacitor configured to: if the input signal is at the sixth logiclevel, be charged by the first current flowing through the firsttransistor; and if the input signal is at the fifth logic level, bedischarged by the second current flowing through the second transistor.16. The system of claim 14, and further comprising: a switch coupledbetween a first input terminal of the comparator and a second inputterminal of the comparator, the comparator further configured to receivethe first voltage signal at the first input terminal and receive thethreshold signal at the second input terminal; wherein the switch isconfigured, if the input signal changes from the fifth logic level tothe sixth logic level, to be closed after a predetermined delay.
 17. Thesystem of claim 16, and further comprising: a signal generatorconfigured to receive the input signal, generate a first signal based onat least information associated with the input signal, and send thefirst signal to the switch; wherein the signal generator is furtherconfigured to, if the input signal changes from the fifth logic level tothe sixth logic level, change the first signal from a seventh logiclevel to an eighth logic level after the determined delay.
 18. Thesystem of claim 17 wherein the signal generator is further configuredto, if the input signal changes from the fifth logic level to the sixthlogic level, after the first signal is changed from the seventh logiclevel to the eighth logic level, change the first signal back to theseventh logic level from the eighth logic level to form a signal pulse.19. The system of claim 17 wherein the switch is further configured to:if the first signal is at the seventh logic level, be opened; and if thefirst signal is at the eighth logic level, be closed.
 20. The system ofclaim 17 wherein the signal generator is configured to generate one ormore pulse-width-modulation signals.
 21. A method for dimming control ofone or more light emitting diodes, the method comprising: receiving athreshold signal and an input signal associated with a TRIAC dimmer;generating a comparison signal based on at least information associatedwith the threshold signal and the input signal; receiving the comparisonsignal; determining a duty cycle of the comparison signal; processinginformation associated with the duty cycle and a threshold value; andgenerating a detection signal based on at least information associatedwith the comparison signal; receiving the detection signal; generatingan output signal based on at least information associated with thedetection signal; and sending the output signal to a switch; wherein theprocess for generating a comparison signal based on at least informationassociated with the threshold signal and the input signal includes: ifthe input signal is larger than the threshold signal in magnitude,generating the comparison signal at a first logic level; and if theinput signal is smaller than the threshold signal in magnitude,generating the comparison signal at a second logic level; wherein theprocess for generating a detection signal based on at least informationassociated with the comparison signal includes: if the duty cycle of thecomparison signal is larger than the threshold value in magnitude,generating the detection signal at a third logic level; and if the dutycycle of the comparison signal is smaller than the threshold value inmagnitude, generating the detection signal at a fourth logic level;wherein the process for generating an output signal based on at leastinformation associated with the detection signal includes if thedetection signal is at the fourth logic level, generating the outputsignal to cause the switch to remain open for a first period of time.22. The method of claim 21 wherein the process for generating an outputsignal based on at least information associated with the detectionsignal further includes, generating the output signal to cause theswitch to remain closed for a second period of time until at least thecomparison signal changes from the first logic level to the second logiclevel.
 23. The method of claim 22 wherein the process for generating anoutput signal based on at least information associated with thedetection signal further includes, if the comparison signal is at thefirst logic level and the detection signal is at the third logic level,generating the output signal to cause the switch to be opened and closedcorresponding to a modulation frequency.
 24. The method of claim 23wherein the first period of time is larger than a modulation periodcorresponding to the modulation frequency.
 25. The method of claim 23wherein the second period of time is larger than a modulation periodcorresponding to the modulation frequency.
 26. A method for detecting aduty cycle of a signal, the method comprising: receiving an inputsignal; generating a first voltage signal based on at least informationassociated with the input signal; receiving the first voltage signal anda threshold signal; generating a comparison signal based on at leastinformation associated with the first voltage signal and the thresholdsignal; receiving the comparison signal and the input signal; andgenerating an output signal based on at least information associatedwith the comparison signal and the input signal; wherein the process forgenerating a comparison signal based on at least information associatedwith the first voltage signal and the threshold signal includes: if thefirst voltage signal is larger than the threshold signal in magnitude,generating the comparison signal at a first logic level; and if thefirst voltage signal is smaller than the threshold signal in magnitude,generating the comparison signal at a second logic level; wherein theprocess for generating an output signal based on at least informationassociated with the comparison signal and the input signal includes: ifa duty cycle of the input signal is larger than a threshold value,generating the output signal at a third logic level; if the duty cycleof the input signal is smaller than the threshold value, generating theoutput signal at a fourth logic level; and if the input signal changesfrom a fifth logic level to a sixth logic level and if the comparisonsignal is at the first logic level, changing the output signal from thethird logic level to the fourth logic level.